### Geologic map of the Alamosa 30’ × 60’ quadrangle, south-central Colorado

By: Ren A. Thompson**Ralph R. Shroba**Michael N. MachetteChristopher J. Fridrich**Theodore R. Brandt**Michael A. Cosca**

                            https://doi.org/10.3133/sim3342

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-                                                                                                                             Document:                                                                                                                                                                                                                                                  **Report**                                                                                                     (11.7 MB pdf)                                                                                                                                     
- Plates:                               - **Map**                            (83 MB pdf)                        
  - **Map with hillshade**                            (106 MB pdf) 
- Dataset:  **Geospatial database**
- Metadata:  **Metadata**
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- Superseded Publications:
                                        Preliminary geologic map of the northwestern part of the Alamosa 30 X 60 minute quadrangle, Alamosa and Conejos Counties, Colorado(2005)                                    

                                        Preliminary Geologic Map of the North-Central Part of the Alamosa 30' x 60' Quadrangle, Alamosa, Conejos and Costilla Counties, Colorado(2008)                                    

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#### Abstract

First posted October 15, 2015

**For additional information, contact:**
Director, Geosciences and Environmental Change Science Center U.S. Geological Survey Box 25046, Mail Stop 980 Denver, CO 80225http://gec.cr.usgs.gov/

The Alamosa 30'× 60' quadrangle is located in the central San Luis Basin of southern Colorado and is bisected by the Rio Grande. The Rio Grande has headwaters in the San Juan Mountains of Colorado and ultimately discharges into the Gulf of Mexico 3,000 kilometers (km) downstream. Alluvial floodplains and associated deposits of the Rio Grande and east-draining tributaries, La Jara Creek and Conejos River, occupy the north-central and northwestern part of the map area. Alluvial deposits of west-draining Rio Grande tributaries, Culebra and Costilla Creeks, bound the Costilla Plain in the south-central part of the map area. The San Luis Hills, a northeast-trending series of flat-topped mesas and hills, dominate the landscape in the central and southwestern part of the map and preserve fault-bound Neogene basin surfaces and deposits. The Precambrian-cored Sangre de Cristo Mountains rise to an elevation of nearly 4,300 meters (m), almost 2,000 m above the valley floor, in the eastern part of the map area. In total, the map area contains deposits that record surficial, tectonic, sedimentary, volcanic, magmatic, and metamorphic processes over the past 1.7 billion years.

#### Suggested Citation

Thompson, R.A., Shroba, R.R., Machette, M.N., Fridrich, C.J., Brandt, T.R., and Cosca, M.A., 2015, Geologic map of the Alamosa 30’ × 60’ quadrangle, south-central Colorado: U.S. Geological Survey Scientific Investigations Map 3342, 23 p., scale 1:100,000, https://doi.org/10.3133/sim3342. (Supersedes Open-File Report 2005–1392, and Open-File Report 2008–1124.)

ISSN: 2329-132X (online)

#### Study Area

#### Table of Contents

- Introduction
- Description of Map Units
- Acknowledgments
- References Cited

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