WSPC02847

• File Number: 7630.500
• Description: Wild and Scenic - Rio Grande River
• State: CO
• Basin: Statewide
• Date: 9/1/1989
• Author: DOI-BLM
• Title: San Luis Resource Management Plan and Environmental Impact Statement - Draft - Volume I - Introduction-Chapters 1-3
• Water Supply Pro - Doc Type: Report/Study

001771

basement in these basins are 19,000 and 10,000 feet
respectively (Burroughs, 1981).

Overlying these basement bfocks is a thick sequence of
Tertiary age valley-fill sediments and volcanic rock. The
absence of Paleozoic and Mesozoic age sediments within
the larger portion of the San Luis Valley reflects the fact
that throughout much of geologic time it was a positive
feature.

The San Luis Valley is divided into five distinct physiographic
provinces (Upson, 1939); (1) the Alamosa Basin, which
is a broad almost featureless plain of alluvial valley-fill; (2)
the San Luis Hills, which exhibit rugged hills and mesas
of eroded volcanic rock; (3) the Taos Plateau, which consists
of widespread thick basalt flows; (4) the Costi11a Plains,
which, though similar to the A1amosa Basin, differs in that
this is an erosional feature rather than a depositional one;
and (5) the Culebra Re-entrant, which is a topographically
divelre area with elevated footlnl1s near the mountains, an
eroded central depression, and a prominent mesa toward
the valley center.

Fluid Minerals

on and Gas: The Bureau of Land Management administe"
oil and gas resources on approximately 621,000 acres within
the SLRA (520,677 acres are BLM surface lands). As of
December 1987, approximately 250,000 acres were under
lease. There were no producing structures within the planning
area until recently (1985) when an oil and gas discovery
from a fee well established the San Luis Basin as a producing
province. In March 1986, BLM approved the South Fork
Oil and Gas Development Contract involving approximately
770 000 acres of U.s. Forest Service, BIM, and State of
Col~rado lands in Archuleta, Conejos, Mineral, Rio Grande,
and Saguache Counties. This development contract defines
exploration objectives, sets time frames, and es!'1~lis~es
financial expenditure requirements for the parltClpating
parties.

This contract does not require the dril\ing of exploration
wells, and geophysical investigations have so far beeo the
principal method utilized in meeting the exploration
requirements. This is reflected in the fact that an average
of five notices per year for geophysical operations have been
received in the SLRA since 1985; however, during the period
1975 to 1985 there were no permits filed. Exploration dril\ing
within the planning area has been extremely limited with
only 20 wells (2 Federal) completed in the approximately
2,500 square miles of the basin. This basic lack of exploration
has essentially left the basin a frontier regioo for oil and
gas exploration with a low to moderate potential for oil
and gas resources (Map 2-3a).

AFFECfED ENVIRONMENT

The San Luis Resource Area can be broken into two separate
areas for ease of discussion concerning the oil and gas
resource potential, These areas are the San Luis Basin and
the San Juan Sag, and a short discussion of each follows:

Son Luis Basin: The faulting and rifting of the Sangre de
Cristo uplift resulted in the formation of the San Luis Basin.
This basis was then iilled by Tertiary clastic and volcanic
rocks to a depth of approximately 20,000 feet adjacent to
the Sangre de Cristo Mouotains. This basin fill can be divided
into four units consisting in descending order as the Alamosa
Formation, the Santa Fe Formation, an unnamed Paleocene
to Eocene unit, and the Vallejo Formation. Potential trapping
mechanisms consist of pinchouts and truncations, fault traps,
and structural closures.

Son Juan Sag: This foreland basin, formerly adjacent to
and west of the Laramide Sangre de Cristo Uplift, remained
intact following formation of the San Luis Basin to the
east This basin was then concealed by more than 10,000
feet of volcanic and volcaniclastic rock with only a small
window of Creataceous rock exposed near Quartz Creek
to indicate the potential sedimentary sequence buried beneath
this volcanic cover. The potential stratigraphic sequence
beneath the volcanic cover could involve Paleozoic (Permo-
Pennsylvanian), Jurassic, Cretaceous, and Tertiary
sediments. Recent exptoration drilliog has confirmed the
presence of a sedimentary sequence for this region. The
completion oflbe Kirby Petroleum Company No. I Jynoifer
well northwest of Del Norte, Colorado, with an initial
production of 30 barrels of oil and 80 MCFGPD, established
the first production of oil and gas within the San Luis Valley.

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GeotbermaI: The San Luis Valley as indicated is a structural,
sediment-filled basin within the Rio Grande Rift Zone (Map
2-3b). This rift zone represents one of the more promising
geothermal resource areas in Colorado because of: (I) recent
volcanism and other igneous activity; (2) tectonic activity
resulting in numerous faults extending to depth; (3) high
heat flow values present; (4) good reservoir rocks and a
trapping mechanism; and (5) a good source of available
,water. With the presence of these features essentially located
throughout the basin, the potential for the presence of this
resource is evident; however, a determination of specific
areas for development is difficult because of a lack of
avai1able subsurface and geophysical data. The use of surface
expressions in the form of hot springs, therefore, is the most
readily available means for identifying areas of geothermal
potential. Table 2-6 lists the currently known geothermal
springs and wells within the San Luis Planning Area.

As of December 1987, there was one geothermal lease
currently existing in the planning area consisting of 2,242

2-9