NEW MEXICO BUREAU OF GEOLOGY AND MINERAL RESOURCES A DIVISION OF NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
107°7'30"W
304000
305000
306000
107°5'0"W
307000
308000
309000
310000
107°2'30"W
311000
312000
313000
314000
NMBGMR Open-file Map Series
OFGM 118
Last Modified May 2006
107°0'0"W
315000
DESCRIPTION OF MAP UNITS:
3778000
3778 000
34°7'30"N
34°7'30"N
POST-SANTA FE GROUP UNITS
af
Artificial fill (uppermost Holocene)— Compacted fill as roadway subgrades along U. S. Highway 60;
also earthen dams at stock reservoirs. Thickness 0–6m.
Qvy
Younger valley alluvium, piedmont facies (Holocene to uppermost Pleistocene) — Active channel, low
terrace and alluvial-fan deposits of tributary arroyos. Consists of poorly sorted, non-indurated, volcanicrich gravel, sand, silt, and clay. Associated with low graded surfaces formed during last major episode of
valley entrenchment and backfilling. Thickness 0–30 m.
Younger piedmont-slope alluvium (Holocene to upper Pleistocene)¾ Pebbly to sandy alluvial fan and
arroyo-fill deposits on piedmont slopes; includes thin veneers of eolian sand. Graded to the closed basin
floor at La Jencia basin playa. Probably less than 20 m thick.
Playa lake deposits (Holocene to upper Pleistocene)—Unconsolidated mud, silt and sand in the playa
lake depression of the central La Jencia Basin. Depression probably formed by ongoing southwest tilt of
the La Jencia Basin (tilted fault block) combined with northeast progradation of the Water Canyon alluvial fan (Qvo3) in middle to late Pleistocene time. Probably 10-20 m thick.
Eolian deposits (Holocene to upper Pleistocene) — Light gray to pale red, fine-grained, well-sorted,
wind-blown sand. Small dune fields locally cap older surfaces at slope breaks east of the La Jencia playa
and NE of larger arroyos. Thickness range: 0–3 m.
Colluvium and minor alluvium, undifferentiated (Holocene to middle Pleistocene) —Colluvium and
talus on steep to moderate slopes in the western Socorro Mountains, Lemitar Mountains and around Water Canyon Mesa. Gravelly colluvium is typically shown where it masks playa deposits of the Popotosa
Formation (Tpp) . Widespread colluvial veneers on dissected piedmont slopes near Sedillo Hill are generally not delineated. Includes minor alluvium on gentler slopes and in narrow drainages. Usually 0.3-3
m. thick, locally as much as 10 m. thick.
Landslide deposits and colluvium (upper to middle Pleistocene) — Slump blocks and toreva blocks
(rotated blocks) of lava (derived from Tbsh, Tsrd, Tsd and Tsr) have slipped down slope on underlying
Popotosa playa deposits (Tpp). Suffix indicates composition of slide blocks (Qlb= basaltic andesite, Qld=
dacite/rhyodacite, Qlr=rhyolite). Slide blocks and mudstones are mantled by abundant colluvium. Includes small mudflows and minor alluvium. Slide areas are generally inactive at present. Widespread
around Strawberry Peak, Sedillo Hill and western Socorro Mountains. Characterized by hummocky topography. Thickness of lava slide blocks is as much as 90 m.
Fill of small playas in landslide terrane (Holocene to middle Pleistocene)—Unconsolidated mud, silt
and sand in small closed basins on upslope side of toreva blocks. Probably less than 10 m thick.
Older valley alluvium, piedmont facies (upper to middle Pleistocene) — Inset terrace and alluvial-fan
deposits of tributary arroyos associated with five episodes of valley entrenchment and backfilling. From
oldest to youngest, graded surfaces associated with these alluvial deposits project: 64–70 m (Qvo1), 43–
52 m (Qvo2), 30–40 m (Qvo3), 15–21 m (Qvo4) and 6–9 m (Qvo5) above the modern floodplain of the
Rio Grande in the Socorro 7.5' Quadrangle (Chamberlin, 1999). The height of alluvial surfaces above
modern drainages progressively decreases upslope into the Water Canyon quadrangle. The top of Qvo1
stands about 15-18m above the floor of Sixmile Canyon. Large alluvial fans from South Canyon and
Water Canyon are graded to a higher base level (Nogal Canyon box) than Sixmile Canyon. Consists of
poorly to moderately sorted, bouldery to cobbly, volcanic-rich gravel, gravelly sand and muddy silts.
Generally reddish orange to reddish brown, locally light brown to tan in color. Mostly nonindurated,
however, uppermost beds beneath graded surfaces are variably cemented by pedogenic carbonate horizons (c) approximately 0.6 m to 0.1 m thick. Correlation with alluvial units in Socorro Quadrangle is
based on lateral continuity along Socorro Canyon and Sixmile Canyon drainages. Tentative correlation
with Quaternary alluvial units in the San Acacia and Las Cruces areas (based on projected height above
Rio Grande and level of soil development) suggest these deposits range in age from middle to late Pleistocene (250,000 years to 25,000 years old; Machette, 1978). Thickness 0–12 m, average thickness 6–9 m.
Qpy
3777000
3777 000
Qpl
Qe
Qca
3776000
3776 000
Ql
Qp
3775000
3775 000
3774000
Qvo
3774 000
Qpo3
34°5'0"N
000
3773
34°5'0"N
3773000
3772000
Qsh
3771000
3771 000
3770000
3770 000
Qsp
QTsp
3769000
3769 000
34°2'30"N
34°2'30"N
3768000
3768 000
3767000
3767 000
3766000
3766 000
3765000
3765 000
3764000
34°0'0"N
3764 000
Tpp
Tpc_
Tpd_
Older piedmont-slope alluvium (middle Pleistocene)— Bouldery to sandy alluvial-fan deposits graded to
the central bolson of La Jencia Basin. High-gradient fans emanate from Shakespeare, Garcia and Jordan
canyons. Fan deposits disconformably overlie thick piedmont deposits of the Sierra Ladrones Formation
(QTsp) that are lithologically very similar, since they have the same provenance. Basal unconformity not
exposed; probably 3-10m thick.
SANTA FE GROUP
Intermontane basin fill of the Rio Grande rift. As redefined by Machette, 1978, includes the Pliocene and
Pleistocene valley fill of the Sierra Ladrones Formation (of Machette, 1978), and Miocene bolson fill of
the Popotosa Formation, named by Denny, 1940. Also includes intercalated volcanic units such as the
Socorro Peak Rhyolite, rhyolitic ash-falls, and local basalt flows (Osburn and Chapin, 1983).
UPPER SANTA FE GROUP:
Qsh
Sierra Ladrones Formation (lower Pleistocene to lower Pliocene) — Late-stage
Qsp
QTsp
basin fill of the Rio Grande valley characterized by an axial-river facies (ancestral
3772 000
Tpcu
Rio Grande) and intertonguing piedmont facies (large alluvial fans) derived from adjacent mountain
ranges. In the Socorro Basin it is capped by Las Cañas geomorphic surface (Qlc) of McGrath and Hawley, 1987. In the La Jencia Basin (Water Canyon quadrangle) only the piedmont facies (QTsp) is exposed under the Sedillo Hill surface (Qsh) of McGrath and Hawley, 1987). QTsp disconformably overlies the 6.9 Ma basaltic trachyandesite of Sedillo Hill (Tbsh) and underlying playa claystones (Tpp) of
the upper Popotosa Formation at the SE margin of the La Jencia Basin. Regional map data indicate that
laterally equivalent piedmont deposits (shed from the eastern Magdalena Mountains) intertongue with
ancestral Rio Grande deposits in the Socorro Basin. Hence the piedmont facies in the La Jencia Basin is
correlative with piedmont facies in the Socorro Basin. Maximum thickness of Sierra Ladrones Formation
in southern La Jencia Basin is about 330m.
Sedillo Hill geomorphic surface of McGrath and Hawley, 1987 (lower Pleistocene ) —
Erosional remnants of constructional alluvial fan surface preserved between the mouth of Sixmile Canyon
and the top of Sedillo Hill. From 6500 to 6100 feet elevation (227 ft/mi) the surface projects eastward as
a concave -upward slope that is continuous with the Las Canas surface at 5200-5100 ft (166 ft/mi) as
mapped in the Socorro quadrangle (Chamberlin, 1999). Surface represents maximum level of aggradation
of late Cenozoic basin fill along the Rio Grande valley near Socorro. Defines top of Santa Fe Group and
Sierra Ladrones Formation where present. Characterized by a dark reddish brown clay-rich soil nearly 2
m thick (Ustollic Paleargid; McGrath and Hawley, 1987). Correlation with Las Canas surface in Socorro
quadrangle is based on projection of graded surface and similar degree of soil development. In comparison, petrocalcic carbonate soils are typical of the Las Canas surface, which occurs at significantly lower
elevations than the Sedillo Hill surface. Sedillo Hill and Las Canas surfaces are tentatively correlated
with the lower La Mesa surface of the Las Cruces area, which has recently been dated at 0.73–0.9 Ma
(Mack and others, 1993).
Sierra Ladrones Formation, piedmont facies, upper (lower Pleistocene)— Pebbly to sandy alluvialfan deposits, arroyo-fill deposits and interbedded fine-grained eolian sands. Deposits were graded from
southwestern Lemitar Mountains to floor of La Jencia Basin prior to incision along San Lorenzo Arroyo
and La Jencia Creek (early Pleistocene time). Basal beds probably conformable on QTsp. Graded slopes
indicate paleocurrent directions. Steeper slopes (~2°) on east flank of La Jencia Basin probably reflect
about 1° westerly tilt in middle to late Pleistocene time. Includes thin veneers of upper Pleistocene eolian
sands that are generally not shown. Exposed thickness less than 30 m.
Sierra Ladrones Formation, piedmont facies (lower Pleistocene to lower Pliocene) —Piedmont-slope
deposits below Sedillo Hill geomorphic surface of McGrath and Hawley, 1987. Consists of reddish orange to reddish brown, poorly consolidated, volcanic-rich, boulder to cobble conglomerates and conglomeratic sandstones and sandstones. Buried calcic soil horizons (bc) are locally present. Maximum
thickness of piedmont facies, estimated from cross section, is about 330 m. Wedge-shaped unit thickens
rapidly westward on hanging wall block of the La Jencia fault; approximately 9-12m thick on footwall
block of La Jencia fault near mouth of Sixmile Canyon.
LOWER SANTA FE GROUP:
Tp_
Popotosa Formation (lower to upper Miocene; basal graben fills may be of late Oligocene age?)— Intermontane bolson fill deposits of early Rio Grande rift grabens and tilt-block basins. Defined by Denny,
1940, and redefined by Machette, 1978. In the San Lorenzo Spring quadrangle, north of Water Canyon,
the Popotosa Formation is locally divided into lower conglomeratic piedmont facies (Tpx, Tpd, Tpc) and
upper conglomeratic piedmont facies (Tpcu) on the basis of clast suites (cf. Bruning, 1973) and relative
stratigraphic position to dated lavas and ash beds. The 15.4-Ma “Silver Creek Andesite” (Chamberlin
and McIntosh, unpublished data) and several water-laid ash beds (0-3 m thick) that include pumiceous
sandstones (15.6- 14.5 Ma; Cather et.al., 1994; Cather and Read, 2003) are interbedded in the medial to
upper Popotosa Formation. Similar stratigraphic relationships extend southward into the Water Canyon
Quadrangle. The dated strata indicate a middle Miocene age for the medial and upper Popotosa Formation in the San Lorenzo Spring Quadrangle (Chamberlin, 2004) and correlative water-laid ash beds occur
in the Canoncito de las Cabras area of the Lemitar quadrangle (Chamberlin et.al, 2001). An angular unconformity of 10–25 degrees is evident at the base of the lower Popotosa Formation in the southern
Lemitar Mountains and Water Canyon Mesa. Basal Popotosa debris flows and conglomerates are widely
potassium metasomatized and often very well indurated with jasperoidal silica (Chapin and Lindley,
1986; Dunbar et al, 1994; Dunbar and Miggins, 1996; Chamberlin and Eggleston, 1996, Lueth et.al,
2004). Metasomatic adularia in the lower Popotosa near Socorro Canyon, yields a 40Ar/ 39Ar age of 7.4
±0.1 Ma (Dunbar and Miggins 1996). In the Water Canyon Mesa area, metasomatic adularia yields a
minimum age of 14.1 ± 0.1 Ma (Wilks and Chapin, 1997; So-276), which implies that metasomatism and
hydrothermal alteration may be somewhat older here (e.g. middle Miocene). Assuming concealed faults
in the floor of La Jencia Basin (Chamberlin, 2004), the Popotosa Formation is probably a maximum of
about 2 km thick under the La Jencia playa. Gravity maps (Sanford, 1968) indicate that basin-fill units
thin southward toward the narrow graben between the mouth of Sixmile Canyon and Sedillo Hill (SE
Water Canyon quadrangle). Map units developed in the San Lorenzo Spring quad extend into the northeastern Water Canyon quadrangle.
Tpx
Tpu
Popotosa Formation, upper, conglomeratic sandstone facies (middle to upper Miocene)— Lightbrownish gray to light gray, heterolithic, conglomeratic sandstones, sandstones and minor mudstones.
Characterized by wide variety of volcanic pebbles and minor cobbles representing the entire middle Tertiary volcanic pile; locally contain minor non-volcanic clasts. Conglomeratic beds near Strawberry Peak
are usually well cemented by carbonate. Conglomerate beds are commonly clast supported; low-angle
trough crossbeds (cut and fill) and planar beds are common. Near Strawberry Peak, crystal-rich and crystal-poor ignimbrite pebbles (Hells Mesa-type and La Jencia type) are relatively common (5-10%) as are
vesicular mafic lavas. Northeasterly to easterly paleocurrents and clast lithologies are consistent with a
deeply dissected source highland near Magdalena. Unit appears to occur stratigraphically below or interbedded with thick playa deposits (Tpp) that contain upper Miocene rhyolite lavas (Tsr) and coeval ash
beds in the western Socorro Mountains. Maximum exposed thickness west of Strawberry Peak is 120 m;
may be as much as 600 m thick under Strawberry Peak. Unit thins and grades into playa deposits toward
Socorro Peak.
On Water Canyon Mesa, this unit consists of unconsolidated or poorly cemented gravels, which also
contain a wide variety of volcanic cobbles and pebbles. A distinctive "turkey track" (coarsely porphyritic) andesite clast that occurs in these gravels implies a northeasterly paleocurrent direction. This turkey
track andesite is only exposed about 6 km to the southwest (south of North Baldy). Approximately 60120 m thick on Water Canyon Mesa.
Popotosa Formation, playa facies (upper Miocene)—Mostly red or maroon claystone with minor
greenish claystone and thin bedded buff to light gray siltstones to fine-grained sandstones. Gypsum and
selenitic veinlets are widespread in this unit. Claystones are poorly indurated and commonly masked by
landslide deposits (Qls) and colluvium (Qca) where they underlie steeper slopes on west flank of Socorro
Peak. Playa deposits contain lavas and ash beds ranging from 9.8 to 7.8 Ma (Chamberlin, 1999). The
youngest known playa deposits locally underlie the east flank of Sedillo Hill, which is capped by a basaltic trachyandesite lava flow dated at 6.88 ± 0.02 Ma (W. C. McIntosh and R.M Chamberlin, unpublished data). Maximum thickness estimated from geothermal boreholes north of Sedillo Hill (Chapin et
al. 1978) and a cross section of the western Socorro Mountains is 750 m.
Popotosa Formation, lower, conglomerates and conglomeratic sandstone facies (lower to middle
Miocene)¾ Pale reddish gray, purplish gray, light gray and light brownish gray conglomerates and conglomeratic sandstones. Conglomerates are mostly clast supported and crudely bedded to planar bedded.
Three distinct sub-units (overlapping fan lobes?) are recognized near San Lorenzo Spring (Chamberlin,
2004). The lowest unit consists of pale red to purplish gray, basaltic-andesite dominated conglomerates
with sparse vein quartz and white felsite clasts (Tpc1). A medial sub-unit consists of pale red conglomerates that contain subequal South Canyon Tuff and basaltic andesite clasts (Tpc2). The highest unit is a
light to medium brown boulder to pebble conglomerate containing dominantly South Canyon Tuff clasts
with less abundant basaltic andesites and sparse flow-banded rhyolites (Tpc3). All these conglomerate
sub-units underlie the 15.4-Ma Silver Creek Andesite. Another light brown conglomeratic sandstone unit
(Tpc4) is similar to a mixture of Tpc3 and Tpc1. Tpc4 occurs stratigraphically above the Silver Creek
Andesite and appears to grade southwards into a stratigraphically higher Tpc1 type conglomerate. Subunits 0- 200 m thick. Tpc3 ,Tpc4 and upper Tpc1 are present in the Water Canyon quadrangle; lower
Tpc1 and Tpc2 are absent in the Water Canyon quadrangle.
Popotosa Formation, lower, debris-flow and conglomerate facies (lower to middle Miocene)—Mostly
well indurated, medium reddish brown to dark red, volcanic-rich, matrix supported, debris flows, conglomerates and minor fluvial conglomeratic sandstones. Commonly well cemented by red jasperoidal
silica, which is demonstrably associated with potassium metasomatism in the Socorro quadrangle
(Chamberlin, 1999). Cobble sized clasts are common; boulder beds occur locally near the base. Locally
divided into three overlapping sub-units based on the dominant type of volcanic clasts. Deposits dominated by gray, iddingsite-bearing La Jara Peak Basaltic Andesite clasts are designated Tpd1; deposits
dominated by light-gray South Canyon Tuff clasts are designated Tpd2; and deposits dominated by andesite porphyry clasts (Tar-type) are designated Tpd3. Tpd2 is present in the southern Lemitar Mountains;
Tpd1 and Tpd3 are absent here. Sub-units grade laterally from one composition to another where facies
boundaries are shown; debris-flow units also grade laterally into compositionally equivalent conglomerates. Units fill narrow north-trending fault-block depressions in the southern Lemitar Mountains; northerly paleocurrents are dominant here. Thickness of wedge-shaped fills is highly variable, from 0–300 m.
An angular unconformity at base of Tpd2 truncates a south facing monocline of late Oligocene age (TluTsc age) in the southwestern Lemitar Mountains.
On Water Canyon Mesa, Tpd2 contains abundant clasts of South Canyon Tuff, basaltic andesites,
Lemitar Tuff and porphyritic dacite (Twcm) consistent with a local provenance. Unit ranges from 0-150
m thick in the Water Canyon Mesa area. Tpd2 and all underlying volcanic strata on Water Canyon Mesa
are potassium metasomatized; the minimum age of potassium metasomatism on Water Canyon Mesa is
14.1 Ma.
Popotosa Formation, basal colluvial breccias and debris-flow deposits (upper Oligocene? to lower
Miocene?) ¾Coarse, blocky, volcanic-derived, monolithic and heterolithic breccias and matrix-supported
conglomerates; commonly fill narrow fault-block basins of the early Rio Grande rift. Locally well exposed along the walls of South Canyon. Clast lithologies include angular fragments of South Canyon
Tuff, Lemitar Tuff, and andesite (Tam) that are typically well cemented by red jasperoidal silica. Breccias and conglomerates are 10-30m thick near South Canyon. Breccias and overlying dacitic lava (Twd)
appear to fill a NE-trending, 50-100 meter deep, paleovalley that cuts across north-trending fault blocks
on the north side of South Canyon.
Tsr4
Tsr3
Tsrd
Trt
Twcm
Socorro Peak Rhyolite: cluster of Late Miocene silicic lava domes centered near Socorro Peak (Osburn
and Chapin, 1983). Individual lava domes range in composition from hornblende dacite (69–70% SiO2)
to hornblende-biotite rhyodacite (70–73% SiO2) to high silica-rhyolite (75–77% SiO2); compositional
data from Bobrow, 1983. Dacitic domes are stratigraphically the oldest, rhyodacites are slightly younger,
and rhyolites are associated with 4 younger eruptive centers. The more southerly eruptive centers for
dacites and rhyolites appear to be the most siliceous. Pumiceous ash beds and bedded tuffs of dacitic to
rhyolitic composition are locally mapped as tephra facies (t) of the Socorro Peak rhyolitic that are interbedded in the Popotosa Formation. Tuffs, lavas and associated shallow intrusions (Tid, Tir) are informally subdivided into three members: 1) early dacites (~9.6 Ma), 2) medial rhyodacites (~9.5 Ma), and
3) rhyolites of 4 different eruptive centers ranging in age from 8.8 to 7.0 Ma. Only the two younger rhyolites are present in the Water Canyon quadrangle.
Socorro Peak Rhyolite, Rhyolite of “Tripod Peak” member (upper Miocene)—Light gray, light
brownish gray, and pinkish gray, moderately phenocryst rich (~15%), flow banded, low-silica rhyolite
(72–73% SiO2; Bobrow, 1983). Contains moderately abundant fine to medium-grained phenocrysts of
plagioclase, sanidine and biotite with minor quartz. Tripod Peak lavas are petrographically similar to
slightly older lavas from the "Jejenes Hill" eruptive center (Tsr3). Basal flow boundary with the older
rhyolite (Tsr3) is locally marked by breccia and ash zone that tends to form a recessive slope. Flow units
of Tripod Peak center (Socorro quadrangle, Chamberlin, 1999) yield 40Ar/39Ar ages from sanidine of 7.02
± 0.05 Ma and 7.06 ± 0.03 Ma (Newell, 1997). Rhyolitic surge deposits (Tsrt) and rhyolitic debris-flow
conglomerates (Tsrc), locally exposed under the west dipping basaltic andesite of Sedillo Hill, are interpreted as pyroclastic and epiclastic facies from the Tripod Peak eruptive center.
Rhyolite of Socorro Peak, Rhyolite of “Jejenes Hill” member (upper Miocene)—Light gray, light
brownish gray and pinkish gray, moderately phenocryst-rich (~15%), flow banded, rhyolite lavas (low
silica-rhyolite 71–73% SiO2; Bobrow, 1983). Contains moderately abundant, fine- to medium-grained
(0.5–2 mm) phenocrysts of plagioclase, sanidine and biotite with minor quartz (~1%). Lava domes at
"Jejenes Hill" and unnamed hill to north (6542 ft elevation) represent local source vents. Includes moderately eroded lava flow in low rolling hills to east of "Jejenes Hill". Yields two analytically equivalent
40
Ar/39Ar ages of 7.52 ± 0.09 and 7.45 ± 0.08 Ma from sanidine (Newell, 1997). Flow unit boundaries
(margins) are locally marked by breccia and ash zones, which tend to form recessive slopes. Maximum
thickness of "Jejenes Hill" lava dome is about 270 m.
Socorro Peak Rhyolite, rhyodacite member at Strawberry Peak (upper Miocene)—Mostly pale red to
light gray rhyodacite porphyry lavas containing about 10 percent fine to medium grained phenocrysts of
plagioclase with minor hornblende and biotite (subequal). Larger plagioclase phenocrysts are strongly
resorbed and hornblende commonly shows a magmatic reaction to form biotite. The deeply eroded flow
dome at Strawberry Peak appears to be compositionally zoned (69.8–71.1% SiO2) from dacite to low
silica rhyolite (Bobrow, 1983); hence the compositional name is rhyodacite. Biotite from a slide block
east of Strawberry Peak yielded a 40Ar39Ar age of 10.56 ± 0.11 Ma (Newell, 1997); however this date
must be inaccurate because the rhyodacite at Strawberry Peak overlies the 9.77 Ma basaltic andesite of
Kelly Ranch (Chamberlin, 1999). Biotite from the rhyodacite flow at Radar Peak has yielded an 40Ar/39Ar
age of 9.51 ± 0.06 Ma, which appears to be in agreement with other dated units nearby (Chamberlin,
1999). The Strawberry Peak dome, as much as 220 m thick, was probably emplaced at about 9.5 Ma.
Socorro Peak Rhyolite, dacite member (upper Miocene)—Mostly medium gray to reddish brown dacitic porphyry lavas containing about 10 percent fine to medium grained phenocrysts of plagioclase and
minor hornblende; biotite if present is rare (<0.5%). Medium-grained plagioclase phenocrysts are
strongly resorbed and distinctly less abundant than fine-grained plagioclase phenocrysts. "Smooth Dome"
is at the north end of a NNW-trending intrusive belt of early dacite domes. The dacite at M Mountain has
yielded an apparently spurious 40Ar/39Ar age of 11.56 ± 0.9 Ma from biotite (see Fig. 1). Dacite lavas in
the Socorro Peak area are younger than the basalt of Kelly Ranch (9.77 Ma) and older than the rhyolite at
Signal Flag Hill (8.66 Ma). They are tentatively estimated to be about 9.6 million years old (Chamberlin,
1999). Individual dacitic flows average about 60–120 m in thickness. Thickness range: 0–120 m.
Rhyolitic tuffs of uncertain correlation (middle to upper Miocene) —Thin-bedded fall-out tuffs and
interbedded poorly welded ash-flow tuffs exposed on north flank of Water Canyon Mesa; buff to pale
red. Rhyolitic composition indicated by sparse, small phenocrysts of quartz and feldspar. May be correlative with pyroclastic phase of rhyolite intrusive domes on Water Canyon Mesa (Trw) or possibly with
distal rhyolitic tuffs associated with the rhyolite of Pound Ranch. Thickness from zero to 15m.
Rhyolite of Water Canyon Mesa (lower Miocene) —Dense, pinkish gray to grayish red lava flows of
rhyolitic to dacitic composition. Finely flow banded to weakly foliated lavas contain moderately abundant to abundant (15-40%) phenocrysts of plagioclase, biotite and hornblende. The absence of
phenocrystic quartz suggests a dacitic composition. Most outcrops are potassium metasomatized, which
is characterized by chalky altered plagioclase (replaced by clays and adularia) and oxidized hornblende.
Appears to locally fill a NE-trending paleovalley about 100m deep on the north side of South Canyon.
Angular clasts of older volcanic rocks that locally occur near marginal contacts may have been incorporated from the underlying breccias (Tpx). Ranges from zero to 180m thick. Phenocrystic biotite from
basal vitrophyre has yielded a K/Ar age of 20.5 ± 0.8 Ma (Osburn and Chapin, 1983). Vitrophyric base,
approximately 2m thick, is locally well exposed at the date locality on the north wall of south Canyon
(Molino Peak quadrangle; 0304675/3763910)
EOCENE-OLIGOCENE VOLCANIC ROCKS OF MOGOLLON-DATIL FIELD:
Note: Oligocene tuffs in the Lemitar and Magdalena Mountains are commonly potassium metasomatized;
phenocrystic plagioclase is typically replaced by metasomatic adularia and clay minerals; sanidine and biotite
are usually not altered. Except where noted otherwise, stratigraphic nomenclature of Eocene-Oligocene volcanic rocks is from Osburn and Chapin, 1983.
Tam
Tsc
Tl3
Outflow Units in Southwestern Lemitar Mountains:
Tsc
Tlp
Tl3
Tlu/Tll
Popotosa Formation, undivided (lower to middle Miocene)¾ Poorly exposed volcanic-rich conglomerates and conglomeratic sandstones on the west flank of Lemitar Mountains. Rounded hills west of the
Lemitar Mountains are generally mantled with colluvial soils that contain abundant volcanic cobbles and
pebbles.
VOLCANIC STRATA WITHIN THE POPOTOSA FORMATION:
Note: except where indicated, stratigraphic nomenclature is from Osburn and Chapin, 1983.
Tbsh
Basaltic andesite of Sedillo Hill-- (formerly the Basalt of Sedillio Hill of Osburn and Chapin, 1983)
(upper Miocene) — Medium gray, massive to vesicular, xenocrystic basaltic trachyandesite lava flows.
Locally erupted from a NNE-trending fissure vent or plug about 2.5 km NE of Sedillo Hill Reservoir
(UTM: 0313700 E, 3767600 N). A mixed magma origin is indicated by sparse fine-grained iddingsite
(after olivine) in a matrix of plagioclase microlites and interstitial clinopyroxene (trachybasalt magmatic
suite) and moderately abundant (3-5%) xenocrysts of plagioclase, sanidine, biotite, hornblende and
quartz (rhyolitic magma suite) that commonly exhibit magmatic reaction rims of very fine clinopyroxene. Small rhyolitic/granitic xenoliths are also present. Maximum thickness near vent is 33m; distal flow
at north end of Sedillo Hill is about 5m thick. Subtle flow foliations visible in the canyon walls are locally contorted and folded; flow fold axes trend ENE. Basaltic cinder beds (Tbsht), preserved west of
the vent, are as much as 100m thick. Unit conformably caps thick playa sequence of the upper Popotosa
Formation and is disconformably overlain by piedmont facies of the Sierra Ladrones Formation. Samples
from the basaltic trachyandesite of Sedillo Hill (n = 4) yield a tightly clustered mean 40Ar/39Ar age of
6.88 ± 0.02 Ma from groundmass separates (W. C. McIntosh and R.M Chamberlin, unpublished data).
Ts__
Tsd
Thrs
Tl2
Tv
Tl1
Tj
Tza
Th
South Canyon Tuff (upper Oligocene)—Partially to densely welded, light gray to pale grayish red,
phenocryst-poor to moderately phenocryst-rich, pumiceous, high silica rhyolite ignimbrite. Medium
grained (1–3 mm) phenocrysts of subequal quartz and sanidine, with traces of biotite and plagioclase;
crystals progressively increase upwards from about 5% near partly welded base to as much as 25% near
densely welded top (where preserved). Sanidine commonly shows blue chatoyancy (i.e. moonstones).
Partially welded, phenocryst-poor, pumiceous basal zone is commonly about 30m thick and grades upwards into densely welded moderately crystal-rich zone. Generally lithic poor except near base; light
gray pumice (1–5 cm) is moderately abundant (5-15%). Represents remnants of outflow sheet erupted
from the Mount Withington caldera in the northern San Mateo Mountains (Ferguson, 1991). Mean
40
Ar/39Ar age is 27.37 ± 0.07 Ma; magnetic polarity is reverse (McIntosh et al., 1991). Correlation here is
based on lithology and relative stratigraphic position. Thickness ranges from 0-90 m.
La Jara Peak Basaltic Andesite, middle and upper tongues undifferentiated (upper Oligocene)—
Basaltic andesite lavas equivalent to Tl2 and Tl3 in the southwestern Lemitar Mountains, where the Lemitar Tuff is missing. The La Jara Peak Basaltic Andesite represents a widespread thick pile of alkaline
basaltic lavas that accumulated on the SE margin of the Colorado Plateau in upper Oligocene time
(Osburn and Chapin, 1983). The pile is locally divided into tongues where thin ash-flow sheets are intercalated with the basaltic pile. Wedge-shaped prisms of basaltic lavas in Lemitar Mountains indicate they
were erupted contemporaneously with early extension and domino-style block rotation in the Lemitar
Mountains (Chamberlin 1983; Cather, et. al., 1994).
La Jara Peak Basaltic Andesite, upper tongue (upper Oligocene)— Mostly medium gray to purplish
gray, massive and platy to vesicular basaltic andesite lavas characterized by moderately abundant (5–
10%) fine- to medium-grained phenocrysts of olivine, usually altered to reddish brown iddingsite.
Phenocrystic plagioclase is typically absent. A black to medium gray olivine-bearing basalt is often present immediately above the Lemitar Tuff Thin flows (3-6m) commonly exhibit vesicular tops and reddish
basal zones. Upper flows are locally interbedded with grayish to reddish brown, fine-grained sandstones
that occasionally contain thin light-colored ash beds. Tl3 is older than South Canyon Tuff and younger
than the Lemitar Tuff. Thickness of wedge-shaped prism usually ranges from 60-330 m. Locally includes
minor andesitic conglomerates (Tl3s) at base of South Canyon Tuff (035000/3764170). Locally truncated
by angular unconformity in SW Lemitar Mountains.
Lemitar Tuff; upper and lower members (upper Oligocene)—Compositionally zoned (77–65 wt%
SiO2), ignimbrite subdivided into a partially to densely welded, light gray, phenocryst-poor (5-15%),
rhyolite lower member (Tll), and densely welded, red to grayish red, phenocryst-rich (30–45%), dacitic
to rhyolitic upper member (Tlu). Contains sparse to abundant, medium-grained (1-4 mm) phenocrysts of
quartz, sanidine, plagioclase (altered), and biotite with traces of augite and sphene. Lower third of upper
member is relatively quartz poor (<5%) compared to upper two thirds, which is quartz rich (10–15%).
Small (1–3 cm) phenocryst-poor pumice is moderately abundant (3–5%) in lower member. Sparse,
phenocryst-rich pumice and small (<2 cm) grayish red “magma clots” of dacite/andesite porphyry are
typical in outflow of the upper member. Basal vitrophyre often occurs where the lower member is absent.
Represents outflow sheet erupted from the Hardy Ridge caldera in the west-central Magdalena Mountains (G. R. Osburn oral commun. 1997, Chamberlin et al, 2004). Lower member (< 40 m) and upper
member (< 50 m) locally wedge out onto paleotopographic highs. Lemitar Tuff fills in tilted early rift
fault blocks in the central Lemitar Mountains (Chamberlin, 1983). Mean 40Ar/39Ar age (bulk sanidine) is
28.00 ± 0.08 Ma ; paleomagnetic polarity is normal (McIntosh and others, 1991). Locally preserved on
down-warped southern side of south-facing monocline in southwestern Lemitar Mountains. Monocline
represents pre-Lemitar uplift on the south followed by post Lemitar subsidence to the south (i.e. precaldera tumescence and post-caldera subsidence).
Sandstone beds of the Hardy Ridge Formation (new name--upper Oligocene) — Red rhyolitic sandstones derived from the underlying upper Lemitar Tuff. 0-10m thick. Lies well outside the Hardy Ridge
caldera, but occupies same stratigraphic position as the thick fill of the Hardy Ridge caldera (Chamberlin
et.al, 2004), which is here recognized as the redefined Hardy Ridge Formation of post Lemitar Tuff age
(not post Hells Mesa Tuff age, as initially defined by Osburn and Chapin, 1983).
La Jara Peak Basaltic Andesite, medial tongue (upper Oligocene)—Mostly medium to dark gray and
purplish gray, platy to vesicular, fine-grained basaltic andesite lavas generally characterized by sparse
small reddish brown phenocrysts of “iddingsite” Generally represents thin flows, stacked one on another,
commonly with vesicular tops and reddish basal zones. Amygdaloidal calcite is common in vesicular
zones. Occurs between Lemitar Tuff and Vicks Peak Tuff. Anomalously thin interval (~10m) on southfacing monocline in SW Lemitar Mountains implies pre-Lemitar uplift here.
Vicks Peak Tuff (upper Oligocene)— Cliff-forming, brown to light brownish gray and light gray,
phenocryst poor, pumiceous, densely welded rhyolite ignimbrite. Distinctive aspects include craggy cliffforming character, pervasive well developed compaction foliation, and large “sandy” (vapor phase) pumice lapilli as much as 30 cm long. Contains 1–5 percent phenocrysts of sanidine and sparse quartz. Represents outflow sheet erupted from the Nogal Canyon caldera in the southern San Mateo Mountains
(Osburn and Chapin, 1983). Mean 40Ar/39Ar age is 28.56 ± 0.06 Ma; paleomagnetic polarity is reverse
(McIntosh and others, 1991). 60-75 m thick.
La Jara Peak Basaltic Andesite, lower tongue (upper Oligocene)—Medium gray to purplish gray,
basaltic andesite lavas characterized by sparse small reddish brown phenocrysts of “iddingsite” (oxidized
and hydrated olivine), locally represents stacked flows. Thickness variations define relative up and down
relationships of early rift normal fault blocks (Chamberlin, 1983). 0-30 m thick.
La Jencia Tuff (upper Oligocene)—Light gray, pale red and grayish red, phenocryst poor, rhyolite ignimbrite, characterized by gray massive basal zone and a medial zone of very densely welded rheomorphic (flow banded) ignimbrite. Flow-banded core grades to normal eutaxitic ignimbrite near base and top.
Contains sparse (3–5%) phenocrysts of sanidine and quartz with traces of plagioclase and biotite. Represents outflow sheet erupted from the composite Sawmill Canyon caldera in the west-central and eastern
Magdalena Mountains (Osburn and Chapin, 1983). Mean 40Ar/39Ar age from bulk sanidine separate is
28.85 ± 0.04 Ma; paleomagnetic polarity is reverse (McIntosh and others, 1991). As much as 120 m thick
in SW Lemitar Mountains
Andesite member of the Luis Lopez Formation, medium porphyritic subunit, (lower Oligocene) —
Dark purplish gray, gray, and reddish brown, medium grained (1–3 mm) andesite porphyry lavas. Massive to platy and locally vesicular lavas contain moderately abundant (5–20%) phenocrysts of altered
plagioclase and pyroxene. Distal flow about 20-30m thick. May represent fill of a paleovalley on north
rim of the Socorro caldera. Fissure vents for equivalent lavas occur in the northern moat of the Socorro
caldera, near Socorro Canyon.
Hells Mesa Tuff (lower Oligocene)— Pale reddish to purplish gray, densely welded, phenocryst-rich (40–
50%), quartz-rich, rhyolite ignimbrite. Typically contains abundant medium grained (1–3 mm)
phenocrysts of sanidine, plagioclase, quartz and minor biotite. Quartz is minor component (1-2%) only in
thin basal zone. Mean 40Ar/ 39Ar age (bulk sanidine) is 32.06 ± 0.1 Ma; paleomagnetic polarity is reverse
(McIntosh et al. 1991). Large volume ignimbrite (1200 km3) erupted from Socorro caldera (Chamberlin
et. al, 2004: McIntosh et. al., 1991). Thickness of outflow sheet in Lemitar Mountains is typically 90-150
m.
Tlu/Tll
Txa
Th
Outflow and Intracaldera Units in Water Canyon Mesa Area:
Andesite member of the "Basalt of Madera Canyon" of Bobrow et.al. , 1983 (upper Oligocene) —
Brownish gray to grayish red porphyritic andesite lavas with sparse to moderately abundant (5-15%)
phenocrysts of plagioclase and pyroxene with minor biotite and quartz. Phenocryst-poor pyroxene andesites tend to occur near the base of the unit and more porphyritic plagioclase andesites are dominant near
the top. Reaction rims around rare quartz crystals suggest that quartz occurs as xenocrysts. Potassium
metasomatism makes primary phenocrystic minerals difficult to recognize. Unit conformably overlies the
South Canyon Tuff and is disconformably overlain basal Popotosa breccias (Tpx) and lavas assigned to
the Rhyolite of Water Canyon Mesa (Twcm). Occupies the same stratigraphic position as plagioclaseolivine andesite, pyroxene andesite, and basaltic andesite lavas previously called the "Basalt of Madera
Canyon" by Bobrow et.al., 1983, which have been recently dated at 26.95 ± 0.2 Ma by the 40Ar/ 39Ar
method (R. Chamberlin and W. McIntosh, unpublished data). "Tam" is interpreted as a more proximal
and evolved portion of the same eruptive series that has been dated at Rincon Madera Canyon, which is
located 5km SE of Water Canyon Mesa. "Basalt of Madera Canyon" is also laterally equivalent to the
upper basaltic andesite unit (Tba2) of Osburn, 1978 as mapped in the Pound Ranch area, north of Rincon
Madera Canyon. Maximum thickness on NE flank of Water Canyon Mesa is 180m; unit is locally truncated by one or more Miocene erosion surfaces.
South Canyon Tuff (upper Oligocene)— Partially to densely welded, light gray to pale grayish red to
chocolate brown (where densely welded), phenocryst-poor to moderately phenocryst-rich, pumiceous,
high silica rhyolite ignimbrite. See description of South Canyon Tuff in the SW Lemitar Mountains for
additional general attributes. In contrast to the SW Lemitar Mountains, lithic-rich zones are commonly
present near Water Canyon Mesa. Some lithic-rich pods contain abundant xenoliths of Lemitar Tuff and
basaltic andesite lava, which together comprise more than 50% of the rock volume in the pod. A ledgeforming lithophysal zone locally marks the transition from the crystal-poor basal zone to the moderatelycrystal rich upper zone of the South Canyon Tuff near Water Canyon Mesa. Abrupt thickness variations
of the underlying basaltic andesite (Tl3) and lithic-rich pods derived from (scoured from?) the underlying
Lemitar Tuff indicate the South Canyon Tuff locally buried east-tilted fault blocks of the early Rio
Grande rift in late Oligocene time (near mouth of South Canyon). Outflow-scale thickness here ranges
from 60-180 m; locally truncated by Miocene erosion surface near Water Canyon.
La Jara Peak Basaltic Andesite, upper tongue (upper Oligocene)— Medium gray basaltic andesite
lavas characterized by moderately abundant (5–10%) fine- to medium-grained phenocrysts of olivine,
usually altered to reddish brown iddingsite. Phenocrystic plagioclase is typically absent. See description
of Tl3 in the SW Lemitar Mountains for additional general attributes. Thickness ranges from 30-120 m;
wedge-shaped prisms locally define east-tilted early rift fault blocks near the mouth of South Canyon.
Tl3 lavas appear to lap onto or wedge out against Hells Mesa Tuff at the northwestern topographic wall of
the Sawmill Canyon caldera, near the Manganese Queen Mine. The presence of this widespread lava
flow unit within and north of the Sawmill Canyon caldera, however, suggests that the Lemitar Tuff buried the north margin of the caldera prior to eruption of the Tl3 lavas. A jasper cemented andesitic conglomerate bed (Tl3s) locally occurs at the top of this unit on the north side of South Canyon.
Lemitar Tuff; upper and lower members (upper Oligocene)—Compositionally zoned (77–65 wt%
SiO2), ignimbrite subdivided into a partially to densely welded, light gray, phenocryst-poor (5-15%),
rhyolite lower member (Tll), and densely welded, red to grayish red, phenocryst-rich (30–45%), dacitic
to rhyolitic upper member (Tlu). See unit description of Lemitar Tuff in the SW Lemitar Mountains for
additional general attributes.
In contrast to the southwestern Lemitar Mountains, the Lemitar Tuff is 2 to 3 times thicker (180-300 m)
near Water Canyon Mesa. Greater thickness here can be attributed to a more proximal position, partial
infilling of a preexisting depression (Sawmill Canyon caldera), and/or local syneruptive subsidence near
the northeastern margin of the Hardy Ridge caldera, which is the source of the Lemitar Tuff. Also, the
uppermost Lemitar Tuff contains larger fragments of very-crystal rich pumice (comagmatic granite [?], 210 cm) and larger mafic clots of comagmatic dacite (2-5 cm), which also reflect a more proximal position
than the southwestern Lemitar Mountains.
Andesite member of the Sawmill Canyon Formation (upper Oligocene) — Multiple flows of medium
gray to purplish gray andesitic lavas that contain sparse to moderately abundant (5-10%) altered
phenocrysts of plagioclase and pyroxene. Base is not exposed in the Water Canyon quadrangle; minimum
(exposed) thickness in eastern Sixmile Canyon is 300m. The Sawmill Canyon Formation represents the
heterogeneous fill of the Sawmill Canyon caldera (Osburn and Chapin, 1983); it age is bracketed by the
underlying 28.9 Ma La Jencia Tuff and the overlying 28.0 Ma Lemitar Tuff (McIntosh et. al., 19991).
Maximum thickness of the Sawmill Canyon is approximately 800m (Osburn and Chapin, 1983).
Hells Mesa Tuff (lower Oligocene)— Densely welded, phenocryst-rich (40–50%), quartz-rich, rhyolite
ignimbrite. See description of Hells Mesa Tuff in the SW Lemitar Mountains for additional general attributes. Bleached, silicified and propylitized Hells Mesa Tuff near the mouth of Water Canyon exhibits
anomalous colors ranging from yellowish brown to pale greenish gray. NNE-trending rhyolite dikes (Tir)
locally cut the Hells Mesa Tuff here and near the Manganese Queen mine. This fault-bounded sliver is
interpreted here as upper caldera-facies Hells Mesa Tuff, just inside the northwestern ring-fracture zone of
the Socorro caldera (cf. Chamberlin et. al, 2004). Thickness uncertain here; the nearest completely exposed intracaldera section at North Baldy is approximately 1100 m thick.
Tertiary Intrusive Rocks
Twr
White rhyolite intrusive lava domes (middle Miocene [?] or possibly late Oligocene) — Light gray to
white, flow-banded rhyolite with sparse to moderately abundant small phenocrysts of sanidine, quartz and
minor biotite. Two "intrusive" lava domes are recognized. The northern dome at Wet Weather Spring is
phenocryst poor. It appears to intrude the South Canyon Tuff and is buried by Popotosa debris-flow deposits (Tpd2) along its western margin. N-trending quartz-barite-pyrite veins occur along this western
margin; pyrite is oxidized to pseudomorphs of goethite and hematite here. The southern dome, located
3km SSW of Wet Weather Spring, is moderately phenocryst rich. It appears to intrude the Lemitar Tuff
and overlying strata as young as the Rhyolite of Water Canyon Mesa (Twcm). Alternatively the apparent
intrusive contacts could be interpreted as younger volcanic strata (post Sawmill Canyon Formation) that
terminated against a buttress unconformity (i.e. crest of steep-sided lava domes). Similar white rhyolite
lava domes are recognized to be onlapped by the Lemitar and South Canyon tuffs in the adjacent Molino
Peak quadrangle (Osburn, 1978; Petty, 1979). Together the two white rhyolite lava domes on Water Canyon Mesa most likely define post-caldera-collapse silicic magmatism along the buried ring-fracture zone
of the Sawmill Canyon caldera, which trends NNE in this area.
Tir
White rhyolite dikes (late Oligocene?) — Light gray to yellowish gray, flow-banded, phenocryst-poor
rhyolite dikes that range in width from 10-100 m. NNE-trending dikes near the Manganese Queen Mine
cut silicified Hells Mesa Tuff. Interpreted as post-collapse ring-fracture intrusions of the 32-Ma Socorro
caldera or possibly the 28.9-Ma Sawmill Canyon caldera. These ring-fracture zones are essentially coincident near the mouth of Water Canyon (see index map, Fig.1).
REFERENCES
Bruning, J. E., 1973, Origin of the Popotosa Formation, north-central Socorro County New Mexico: Ph.D. dissertation, New Mexico
Institute of Mining and Technology, 131 p.; New Mexico Bureau of Mines and Mineral Resources, Open-file Report 42, 110
p.
Cather, S. M., Chamberlin, R. M., Chapin, C. E., and McIntosh, W. C., 1994, Stratigraphic consequences of episodic extension in the
Lemitar Mountains, central Rio Grande rift, in Keller, G. R., and Cather, S. M. (eds.), Basins of the Rio Grande rift: Structure, stratigraphy, and tectonic setting: Boulder, Colorado: Geological Society of America, Special Paper 291, p. 157–170.
Cather, S.M. and Read, A.S., 2003, Preliminary Geology of the Silver Creek 7.5 minute quadrangle, New Mexico; New Mexico Bureau
of Geology and Mineral Resources Open-file Geologic Map, OF-GM-75.
Chamberlin, R. M., 1980, Cenozoic stratigraphy and structure of the Socorro Peak volcanic center, central New Mexico: Ph.D. Dissertation,
Colorado School of Mines, 488 p.
Chamberlin, R. M., 1983, Cenozoic domino-style crustal extension in the Lemitar Mountains, New Mexico: A summary; in Chapin, C.
E., and Callender, J. F. (eds.), Socorro Region II: New Mexico Geological Society, Guidebook 34, p. 111–118.
Chamberlin, R. M. and Eggleston, T. L., 1996, Geologic map of the Luis Lopez 7.5 minute quadrangle, Socorro County, New Mexico: New
Mexico Bureau of Mines and Mineral Resources Open-file Report 421, 147 p.
Chamberlin, R.M., Cather, S.M., Nyman, M.W., and McLemore, V.T., 2001, Preliminary Geologic Map of the Lemitar 7.5'
Quadrangle, Socorro County, New Mexico: New Mexico Bureau of Geology and Mineral Resources Open-file
Geologic Map OF-GM-38, 28 p. 2 plates.
Chamberlin, R..M., McIntosh, W.C. and Eggleston, T.L., 2004, 40Ar/ 39Ar Geochronology and Eruptive History of the Eastern Sector of
the Oligocene Socorro Caldera, Central Rio Grande Rift, New Mexico; in Tectonics, Geochronology and Volcanism in the
Southern Rocky Mountains and Rio Grande Rift: S. M. Cather, W.C. McIntosh and S.A. Kelly (eds.), New Mexico Bureau
of Mines and Mineral Resources Bulletin 160
Chapin, C.E. and Lindley, J.I., 1986, Potassium metasomatism of igneous and sedimentary rocks in the detachment terranes and other
sedimentary basins: Economic implications: Arizona Geological Society Digest, v. 16, p. 118-126.
Denny, C. S., 1940, Tertiary geology of the San Acacia area, New Mexico: Journal of Geology, v. 48, pp. 73–106.
Dunbar, N. W., Chapin, C. E., Ennis, D. J., and Campbell, A. R., 1994, Trace element and mineralogical alteration associated with moderate and advanced degrees of K-metasomatism in a rift basin at Socorro, New Mexico: New Mexico Geological Society
45th Field Conference, p. 225-231.
Dunbar, N. W., and Miggins, D., 1996, Chronology and thermal history of potassium metasomatism in the Socorro, New Mexico area:
Evidence from 40Ar/39Ar dating and fission track analysis (abs.): New Mexico Geology, v. 18, no. 2, pp. 50–51.
Ferguson, C. A., 1991, Stratigraphic and structural studies in the Mt. Withington caldera, Grassy Lookout quadrangle, Socorro County,
New Mexico: New Mexico Geology, v. 13, p. 50-54.
Machette, M. N., 1978, Geologic map of the San Acacia quadrangle, Socorro County, New Mexico: U.S. Geological Survey, Geologic
Quadrangle Map, GQ 1415, scale 1:24,000.
McGrath, D. B., and Hawley, J. W., 1987, Geomorphic evolution and soil-geomorphic relationships in the Socorro area, central New
Mexico; in McLemore, V. T., and Bowie, M. R. (eds.), Guidebook to the Socorro area: New Mexico Bureau of Mines and
Mineral Resources, pp. 55–67.
McIntosh, W. C., Kedzie, L. L., and Sutter, J. F., 1991, Paleomagnetism and 40Ar/39Ar ages of ignimbrites, Mogollon-Datil volcanic
field, southwestern New Mexico: New Mexico Bureau of Mines and Mineral Resources, Bulletin 135, 79 p.
Osburn, G. R., and Chapin, C. E., 1983, Nomenclature for Cenozoic rocks of northeast Mogollon-Datil volcanic field, New Mexico:
New Mexico Bureau of Mines and Mineral Resources, Stratigraphic Chart 1.
Sanford, A.R. 1968, Gravity Survey in central Socorro County, New Mexico Bureau of Mines and Mineral Resources, Circular 91, 14p.
Wilks, M. and Chapin, C.E., 1997, The New Mexico Geochronological Database, New Mexico Bureau of Mines and Mineral Resources, Digital
Data Series, DB1
34°0'0"N
107°7'30"W
304000
305000
306000
307000
107°5'0"W
308000
309000
310000
311000
107°2'30"W
Base map from U.S. Geological Survey 1985, from photographs taken 1978, field checked in 1979, edited in 1985.
1927 North American datum, UTM projection -- zone 13N
1000-meter Universal Transverse Mercator grid, zone 13, shown in red
1:24,000
GRANITE
MOUNTAIN
SAN
LORENZO
SPRING
1
LEMITAR
NEW MEXICO
MAGDALENA
SOUTH
BALDY
WATER
Water
CANYON
Canyon
MOLINO
PEAK
0.5
1000
0
0
1000
2000
3000
1 MILE
4000
5000
6000
312000
313000
LUIS
LOPEZ
QUADRANGLE LOCATION
This draft geologic map is preliminary and will undergo revision. It was produced
from either scans of hand-drafted originals or from digitally drafted original maps
and figures using a wide variety of software, and is currently in cartographic production.
It is being distributed in this draft form as part of the bureau's Open-file map series
(OFGM), due to high demand for current geologic map data in these areas where
STATEMAP quadrangles are located, and it is the bureau's policy to disseminate
geologic data to the public as soon as possible.
After this map has undergone scientific peer review, editing, and final cartographic
production adhering to bureau map standards, it will be released in our Geologic Map
(GM) series. This final version will receive a new GM number and will supercede
this preliminary open-file geologic map.
DRAFT
Magnetic Declination
February, 2005
10º 0' East
At Map Center
0.5
0
7000 FEET
107°0'0"W
May 2006
1 KILOMETER
by
Richard M. Chamberlin1 and G. Robert Osburn 2.
CONTOUR INTERVAL 20 FEET
NATIONAL GEODETIC VERTICAL DATUM OF 1929
New Mexico Bureau of Geology and Mineral Resources
Open-file Map Series
315000
Geologic Map of the Water Canyon 7.5-Minute
Quadrangle, Socorro County, New Mexico
SOCORRO
1
314000
1
2
NMBGMR, 801 Leroy Pl., Socorro, NM, 87801
Earth and Planetary Science Dept., Washington University, St. Louis, MO 63130
OFGM 118
COMMENTS TO MAP USERS
Mapping of this quadrangle was funded by a matching-funds grant from the STATEMAP program
of the National Cooperative Geologic Mapping Act, administered by the U. S. Geological Survey,
and by the New Mexico Bureau of Geology and Mineral Resources, (Dr. Peter A. Scholle,
Director and State Geologist, Dr. J. Michael Timmons, Geologic Mapping Program Manager).
New Mexico Bureau of Geology and Mineral Resources
New Mexico Tech
801 Leroy Place
Socorro, New Mexico
87801-4796
[505] 835-5490
http://geoinfo.nmt.edu
This and other STATEMAP quadrangles are (or soon will be) available
for free download in both PDF and ArcGIS formats at:
http://geoinfo.nmt.edu/publications/maps/geologic/ofgm/home.html
A geologic map displays information on the distribution, nature, orientation, and age relationships
of rock and deposits and the occurrence of structural features. Geologic and fault contacts are
irregular surfaces that form boundaries between different types or ages of units. Data depicted
on this geologic quadrangle map may be based on any of the following: reconnaissance field
geologic mapping, compilation of published and unpublished work, and photogeologic interpretation.
Locations of contacts are not surveyed, but are plotted by interpretation of the position of a given
contact onto a topographic base map; therefore, the accuracy of contact locations depends on the
scale of mapping and the interpretation of the geologist(s). Any enlargement of this map could cause
misunderstanding in the detail of mapping and may result in erroneous interpretations. Site-specific
conditions should be verified by detailed surface mapping or subsurface exploration. Topographic
and cultural changes associated with recent development may not be shown.
Cross sections are constructed based upon the interpretations of the author made from geologic
mapping, and available geophysical, and subsurface (drillhole) data. Cross-sections should be used as
an aid to understanding the general geologic framework of the map area, and not be the sole source
of information for use in locating or designing wells, buildings, roads, or other man-made structures.
The map has not been reviewed according to New Mexico Bureau of Geology and Mineral Resources
standards. The contents of the report and map should not be considered final and complete until
reviewed and published by the New Mexico Bureau of Geology and Mineral Resources. The views and
conclusions contained in this document are those of the authors and should not be interpreted as
necessarily representing the official policies, either expressed or implied, of the State of New Mexico, or
the U.S. Government.
Summary
The Water Canyon quadrangle spans the southern portion of the La Jencia Basin, an active west tilting halfgraben of the Rio Grande rift, which is bound on the west by the Holocene La Jencia fault. West-tilted Tertiary
volcanic strata in the southwestern Lemitar Mountains and the western Socorro Mountains form the east flank of the
La Jencia basin. Volcanic highlands in the footwall of the La Jencia fault (at Water Canyon Mesa) include west and
east tilted extensional fault blocks of the early rift, which locally define the east-northeast trending Socorro
accomodation zone (SAZ; fig 1). Several large displacement, NNW-trending, west-down, normal faults turn
abruptly to the ENE along the accomodation zone between Sixmile Canyon and South Canyon. Wedge-shaped
prisms of basaltic lavas (Tl3) near Sixmile Canyon (A-A') indicate fault blocks south of the SAZ were actively
tilting to the east between 28.0 and 27.4 Ma.
The SAZ has been the dominant locus of silicic volcanism near Socorro for the last 32 million years. Silicic
lava domes (Twcm, Twr) may mark an ENE-trending Miocene intrusive belt along the accomodation zone on Water
Canyon Mesa. Most of the SAZ is now tectonically inactive, except possibly for a short segment between the south
end of the La Jencia fault and the southern Socorro Canyon fault (near Socorro Canyon).
Other important structures in the quadrangle include the 32-Ma Socorro caldera and the 28.7-Ma Sawmill
Canyon caldera (fig.1). An intravolcanic unconformity on the east wall of Water Canyon defines the topographic
wall of the Sawmill Canyon caldera. Hydrothermal alteration and ring-fracture controlled lava domes (Twr) parallel
the caldera wall on Water Canyon Mesa. More widespread potassium metasomatism of Miocene age is dated at a
minimum of 14.1 Ma near South Canyon (Table1). Cliff-forming conglomerates of the Popotosa Formation (Tpd2)
at Water Canyon are cemented by red jasper, which is a known attribute of Miocene potassium metasomatism near
Socorro Canyon and the Tower Mine (fig.1).
Gravels and sands of the upper Santa Fe Group (Sierra Ladrones piedmont facies--QTsp) form a poorly
consolidated aquifer in the southern La Jencia Basin, west of Sedillo Hill (section A-A'). Thick playa claystones of
the upper Popotosa Formation (Late Miocene) underlie the western Socorro Mountains and form a major barrier to
eastward groundwater flow in this area. Some of this eastward flow is forced downward into deep fracture systems
in the underlying Oligocene volcanic rocks. This deeper flow is then forced upward at Socorro Spring where it
appears as warm (90°F) geothermal waters.