New Mexico
Ib uq ue r q ue
corro County
Theprominent saddlein the centralSanMateoMountains, Socorro
County, New Mexico, is causedby a downfaulted block of easily
eroded volcaniclasticsedimentaryrocks called the unit of East Red
Canyon (Ferguson,1985).These rocks are interpreted to be moatfill of a late Oligocene ash-flow-tuff cauldron in the northern San
Mateo Mountains. The cauldron, which was the sourceof the 27.4
Ma (Kedzieet al., 1985)South Canyon Tuff, is currently known to
be smaller and younger than what was originally describedas the
Mt. Withington cauldron by Deal (1973).The southeasttopographic
margin of this cauldron was the major source region for a westfining alluvial-fan complex in the East Red Canyon area. Adjacent
to the topographicmargin, the sedimentary sequenceconsistsmostly
of coarseclast-supporteddebris-flow depositsand fluvial conglomerates.To the west (towardsthe middle of the cauldron)the sequence
is dominatedby medium-grainedcross-stratifiedsandstone,which
is interpretedto be eolian (Fig. 1). The sandstonewas depositedby
prevailing southwestwinds in tabular-planarto wedge-planar sets
up to 20 ft thick (Ferguson,1985).At least 600 ft of these rocks are
exposedalong the walls of EastRed Canyon, the principle drainage
for the east slope of the central San Mateo Mountains.
Oligocene
eolianitesand ichnofo.ssf/s
in the
centralSan MateoMountains
byCharles
A Ferguson,
NewMexico
Bureau
ol Mines
andMineral
Resources,
Socorro,
NM87801
FIGURE l-An exposur,eof eolian sandstone, looking northwest, on the north wall of East Red Canyon just below The Park (sec. 26, T5S R6W
unsurveyed). Six-foot-tall Gunars Berzins is at the base of the cliff for scale.
February 1986 New Mexico Geology
FIGURE2-An inclinedburrow from the upperpart of the unit of EastRed
Canyonin Allen Spring Canyon(sec.35, T65, R6W unsurveyed).The 3inch-wideburrow extendsfrom the top of an eoliansandstonesetthrough
an overlying2-ft-thickbedof air-falltuff. Overlyingthe ashlayer(not shown
in the photograph)
is a bedof massivesandstone.
Theburrowis filledwith
ashwithin the lower sandstone,but in the ashlayerabove,it is filled with
sand.If the burrowwasoccupiedduringdepositionof the air-falltuff, it is
logicalthat the animal(s)would try to escape.
In route to the surfacethe
burrowinganimalwouldhavepushedstopedashto thebottomof itsburrow.
Eventuallythe upper part of the burrow filled with sandfrom above.
The upper part of the unit of EastRed Canyon containsthin sets
of bedded air-fall tuff interlayeredwith sandstone,which preserve
two ichnofossilsfound in Allen Spring Canyon, a tributary to East
Red Canyon. One of the fossils is an inclined burrow with an in-
north. The footprints are on display in the Mineral Museum at the
New Mexico Bureau of Mines and Mineral Resourcesin Socorro.
The inclined burrow and excellentexposuresof eoliansandstoneare
within 0.5 mi walking distancefrom-TurkeySpring, which is at the
end of Cibola National Forestroad 331.
A more detailed description of the unit of East Red Canyon and
the geology of the central San Mateo Mountains is availablefrom
New Mexico Institute of Mining and Technology(Ferguson,1985).
The report will soon be available,in revised form, as iNew Mexico
Bureauof Mines and Mineral ResourcesOpen-file Report.
References
Deal, E G., 1973,Geologyof the northem part of the San Mateo Mountains, Socorro
Counfy, New Mexico-a study of a rhyolite ash-flow tuff cauldron and ihe role of
laminar flow in ash-flow tuffs: Unpublished Ph D dissertation, Universitv of New
Mexico, Albuquerque, 136 pp.
Ferguson,C. A., 1985,Geologyof the east-cenhalSan Mateo Mountains, Socono County,
New Mexico: Unpublished M.S. thesis, New Mexico Institute of Mining and Technology, Socono, 118 pp.
FIGURE 3-Arctiodactyl (spliFhooved mammal) footprint molds
in a slab of bedded air-fall tuff from the upper part of the unit of
East Red Canyon. The two round shapes at the bottom of the
photograph are probably fecal pellet imprints. The pocket knife is
4 incheslong.
New Mexico Geology February 1986
13