GEOLOGY OF THE LA CIENEGA
AREA, SANTA FE COUNTY, N.M.
Daniel Koning and Peggy Johnson
N.M. Bureau of Geology and Mineral Resources
GOALS OF
TALK
• Describe geology of the La Cienega area, with much emphasis on the Ancha Fm
• A topic in next presentation: How does the geology directly influence the locations
of springs and seeps in the La Cienega area?
Three rock packages:
Younger (late rift)
Middle (main rifting)
Older bedrock (pre-rift)
Three rock packages:
Younger (late rift)
Middle (main rifting)
Older bedrock (pre-rift)
Galisteo Formation
•Deposited in a
basin formed
during E-NE
compression 55-37
million years ago.
•Composed of
reddish, cemented
sandstone,
mudstone, and
pebbly sandstone
Galisteo Basin
Three rock packages:
Younger (late rift)
Middle (main rifting)
Older bedrock (pre-rift)
Photos of lithosome E, volcaniclastic sediment
Three rock packages:
Younger (late rift)
Middle (main rifting)
Older bedrock (pre-rift)
The Ancha Fm is a good aquifer – when it is wet!
Base of
Ancha
Formation – a
scoured
unconformity;
commonly
cemented
over bedrock
Alluvial slope deposits in Ancha Fm – lateral textural changes
W
E
downstream
Proximal alluvial slope deposits in Ancha Fm (near Sangre de Cristo Mtns)
Exposure located along Lamy-Santa Fe railroad south of Eldorado. UTM coordinates of
base of section: 3927340 N, 417770 E (NAD 83, zone 13)).
Distal alluvial slope deposits in Ancha Fm (southeast of La Cienega)
On La Cienega on-ramp to I-25. UTM coordinates of base of section: 934548 N, 398323
E (NAD 27, zone 13).
Santa Fe River deposits in Ancha Fm – lateral textural changes
W
E
downstream
Outcrop of Santa Fe River deposits of Ancha Fm overlying lithosome S
of the Tesuque Formation
Fining-upward trend in alluvial slope deposits of Ancha Fm
Thickness trends of the Ancha Formation
Methods
•
•
•
•
The base of the Ancha Formation was mapped using interpretations
of lithologic data from cores, cuttings, geophysical logs, exploration
and water well logs, and outcrop exposures.
The elevation of the Ancha Formation's base in wells and drill holes
was calculated by subtracting the base's depth pick from the surface
elevation.
Base elevation contours were interpolated from point data using a
kriging function in ArcGIS, and smoothed by hand.
Saturated thickness estimates were calculated from a subset of
wells that:
1) penetrate or nearly penetrate the base of the formation;
2) location is well-constrained
3) have an interpretable lithologic record
4) have a reliable water level
Thickness trends of the Ancha Formation
Results
• Santa Fe River deposits are as much as 220 ft thick 1 mi
south-southwest of Agua Fria, but thin westward to 60100 ft under the Caja del Rio Plateau.
• To the south, piedmont deposits are generally 60-150 ft
thick but thicken to 200-295 ft in the center of the
embayment.
• Thickest strata lies near the Santa Fe embayment
syncline, suggesting that tectonic subsidence accounts
for the thicker preservation there.
• Ancha Formation also thickens over paleotopographic
lows and in paleovalleys created by pre-Ancha erosion.
Elevation contour
map of Ancha Fm
base (ft above MSL)
La Cienega
N
1 mile
Isopach map of
Ancha Fm (in ft)
La Cienega
N
1 mile
Ancha Fm
saturated
thicknesses (in ft)
N
La Cienega
1 mile
Formations lying
beneath Ancha Fm
Tesuque Fm,
lithosome S
Tesuque Fm,
lithosome E
interbedded
with basalts
Espinaso
Fm
La Cienega
N
Galisteo Fm
bedrock
1 mile
Espinaso Fm
bedrock
Geology of the La
Cienega area
Take-away points:
•Ancha Fm thins to SW over much
less permeable bedrock
•Ancha Fm is thicker in
paleovalleys, where it is commonly
saturated in its lower part