RATON BASIN

The 'Raton Basin' is a geologic structural basin in southern Colorado and northern New Mexico. In extent, the basin is approximately 50 miles east-west, and 90 miles north-south, in Huerfano and Las Animas Counties, Colorado, and Colfax County, New Mexico.
Although structurally a basin, the Raton Basin forms a topographic high dissected by eastward-flowing streams such as the Purgatoire River. The basin forms the foothills of the Rocky Mountains, immediately east of the Sangre de Cristo Range.
The sedimentary beds that form the basin are of Paleozoic, Mesozoic and Tertiary age. In the eastern part of the basin, the sedimentary section is capped by flows of basalt of Miocene age.^[1] The basin is highly asymmetrical, the beds dipping more steeply on the west side than the east.
The sedimentary rocks of the basin are extensively intruded by igneous plugs, dikes and sills of Eocene to Oligocene age. Two large granitic intrusives near the center of the basin form East Spanish Peak and West Spanish Peak. Dikes of felsic to intermediate composition radiate outward from East and West Spanish Peaks. Dikes of mafic and ultramafic composition trend east-northeast to west-southwest across the basin.^[2] Basaltic sills tend to intrude along the coal beds.
The site of the Raton Basin was a coastal plain at the end of Cretaceous and beginning of Tertiary time, and has a well-preserved sequence of rocks spanning the Cretaceous-Tertiary boundary. For this reason, the Raton Basin had been studied for evidence of the iridium anomaly thought to be evidence for a large meteor impact at the end of the Cretaceous that is thought to have caused the Cretaceous-Tertiary extinction event. The boundary is represented in the basin by a 1-cm thick tonstein clay layer which has been found to contain anomalously high concentrations of iridium. The boundary clay layer is accessible to the public at Trinidad Lake State Park, among other places in the basin.

Contents

Natural Resources

References

Natural Resources

Bituminous coal mines opened in the Raton Basin in 1873. Walsenburg, Colorado, Trinidad, Colorado and Raton, New Mexico became coal-mining towns. The coal deposits are in the Vermejo Formation (Cretaceous) and overlying Raton Formation (Cretaceous and Paleocene).^[3] There are currently no active coal mines in the basin.
A number of wells have been drilled over the years seeking conventional oil and natural gas, but none has been found in economic quantities in the basin.
The first wells were drilled seeking coalbed methane in the Raton Basin in 1982.^[4] Thousands of wells have successfully extracted coalbed methane from the Vermejo Formation and Raton Formation coals. The productive coalbed methane area now covers the central part of the basin, and straddles the Colorado-New Mexico state line.

References

1. Charles L. Pillmore (1991) ''Geology and Coal Resources of the Raton Coalfield'', US Geological Survey, Bulletin 1972(D).
2. Ross B. Johnson (1969) ''Geologic Map of the Trinidad Quadrangle, South-Central Colorado'', US Geological Survey, Miscellaneous Geologic Investigations Map I-558.
3. Ross B. Johnson (1961) ''Coal Resources of the Trinidad Coal Field in Huerfano and Las Animas Counties'', Colorado, US Geological Survey, Bulletin 1112-E.
4. H. Thomas Hemborg (1998) ''Spanish Peak Field, Las Animas County, Colorado'', Colorado Geological Survey, Resource Series 33.