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

Scientific Investigations Map 3342
By: , and 



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, (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
Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic map of the Alamosa 30’ × 60’ quadrangle, south-central Colorado
Series title Scientific Investigations Map
Series number 3342
DOI 10.3133/sim3342
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geosciences and Environmental Change Science Center
Description Report: iv, 22 p.; 2 Plates: 56.00 x 39.74 inches; Metadata; Spatial Data; Read Me
Country United States
State Colorado
Other Geospatial Alamosa, Rio Grand River, San Juan Mountains, San Luis,
Scale 100000
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details