| Abstract: | The map area includes San Luis and the primarily rural surrounding area. San Luis, the county seat of Costilla County, is the oldest surviving settlement in Colorado (1851). West of the town are San Pedro and San Luis mesas (basalt-covered tablelands), which are horsts with the San Luis fault zone to the east and the southern Sangre de Cristo fault zone to the west. The map also includes the Sanchez graben (part of the larger Culebra graben), a deep structural basin that lies between the San Luis fault zone (on the west) and the central Sangre de Cristo fault zone (on the east). The oldest rocks exposed in the map area are the Pliocene to upper Oligocene basin-fill sediments of the Santa Fe Group, and Pliocene Servilleta Basalt, a regional series of 3.7?4.8 Ma old flood basalts. Landslide deposits and colluvium that rest on sediments of the Santa Fe Group cover the steep margins of the mesas. Rare exposures of the sediment are comprised of siltstones, sandstones, and minor fluvial conglomerates. Most of the low ground surrounding the mesas and in the graben is covered by surficial deposits of Quaternary age. The alluvial deposits are subdivided into three Pleistocene-age units and three Holocene-age units. The oldest Pleistocene gravel (unit Qao) forms extensive coalesced alluvial fan and piedmont surfaces, the largest of which is known as the Costilla Plain. This surface extends west from San Pedro Mesa to the Rio Grande. The primary geologic hazards in the map area are from earthquakes, landslides, and localized flooding. There are three major fault zones in the area (as discussed above), and they all show evidence for late Pleistocene to possible Holocene movement. The landslides may have seismogenic origins; that is, they may be stimulated by strong ground shaking during large earthquakes. Machette and Thompson based this geologic map entirely on new mapping, whereas Drenth supplied geophysical data and interpretations. |
| Genre: | USGS Numbered Series |
| ProdID: | 81309 |
| Citation Author: | Machette, Michael N.; Thompson, Ren A.; Drenth, Benjamin J. |
| Citation Contributing Office: | Geological Survey (U.S.) |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | Version 1.0 |
| Citation Editor: | |
| Citation End Page: | |
| Citation Issue: | |
| Citation Keywords: | |
| Citation Language: | ENGLISH |
| Citation Larger Work Title: | |
| Citation LatN: | 0371500 |
| Citation LatS: | 0370730 |
| Citation LonE: | -1052230 |
| Citation LonW: | -1053000 |
| Citation Month: | |
| Citation No Pagination: | N |
| Citation Number Of Pages: | |
| Citation Online Only Flag: | N |
| Citation Phsyical Description: | Map Sheet: 44 x 29 inches; Downloads Directory |
| Citation Projection: | Polyconic |
| Citation Public Comments: | |
| Citation Publisher: | Geological Survey (U.S.) |
| Citation Series: | Scientific Investigations Map |
| Citation Series Code: | SIM |
| Citation Series Number: | 2963 |
| Citation Search Results Text: | Geologic Map of the San Luis Quadrangle, Costilla County, Colorado; 2008; SIM; 2963; Machette, Michael N.; Thompson, Ren A.; Drenth, Benjamin J. |
| Citation Start Page: | |
| Citation Volume: | |
| Citation Year: | 2008 |
| Type: | citation/reference |
| Text: | Geologic Map of the San Luis Quadrangle, Costilla County, Colorado; 2008; SIM; 2963; Machette, Michael N.; Thompson, Ren A.; Drenth, Benjamin J. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/usgs_thumb.jpg |
| URL (INDEX PAGE): | http://pubs.usgs.gov/sim/2963/ |
| URL (INDEX PAGE): | http://ngmdb.usgs.gov/Prodesc/proddesc_83674.htm |
| Date Other: | Fri, 23 May 2008 00:00 -0500 |
| Publisher: | Geological Survey (U.S.) |
