Hydrology of Area 61, Northern Great Plains and Rocky Mountain Coal Provinces, Colorado and New Mexico

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I- IYDROLOGY OF AREA 61, NORTHERN GREAT PLAINS AND ROCKY MOUNTAIN COAL PROVINCES, COLORADO AND NEW MEXICO BY P.O. ABBOTT, ARTHUR L. GELDON, DOUG CAIN, ALAN P. HALL, AND PATRICK EDELMANN Abstract Area 61, one of 20 hydrologic areas of the Northern Great Plains and Rocky Mountain Coal Provinces, is located north and south of the Colora- do -New Mexico State boundary and includes the Raton Mesa coal region. The Huerfano, the Api- shapa, the Purgatoire, the Canadian, the Vermejo, and the Cimarron Rivers are the principal streams draining the region; all are tributaries of the Arkan- sas River. Geologically, the area is an asymmetrical struc- tural trough bounded on the west by the Rocky Mountains and on the east by the Great Plains. There has been abundant igneous activity in the area with the Spanish Peaks and Raton Mesa the most prominent remnants. The Vermejo Formation of Late Cretaceous age and the Raton Formation of Late Cretaceous and Paleocene age are the principal coal- bearing formations. 1 The more than 8,000 feet of topographic relief in Area.61 has a significant impact on the climate and, consequently, on the pattern of stream runoff. Precipitation ranges from less than 16 inches at lower elevations to more than 40 inches on mountain crests. Because a large percentage of the annual runoff comes from snowmelt during spring and early sum- mer months, reservoirs commonly are used to store water in the Plains area .where the long -term average annual precipitation is less than 16 inches. Much of the land in Area 61 is privately owned. Livestock grazing, forest industry, irrigated agricul- ture, recreation, and mining are the principal land uses. Agriculture is the chief use of water. Streamflow is gaged at 52 sites. Streams with headwaters above 10,000 feet generally have a better sustained flow than those with drainage basins at lower elevations. Flash floods with high, sharp peaks and short durations are a problem. Virtually all geologic units in the region yield water to wells. The depth to ground water varies from the land surface to 400 feet. Ground water is both confined and unconfined. The ground -water data base includes 376 sites. Ground water and surface water in Area 61 contain mostly calcium and sodium bicarbonate and sulfate ions; sodium chloride ions locally occur in the ground water. The pH ranges from about neutral to slightly alkaline. Hydrologic problems related to mining activities are erosion and increased sedimentation, local de- cline in the water table, and degradation of water quality. Erosion and sedimentation are primarily surface - mining problems. Sediment yields increase significantly when vegetation is removed from erodi- ble soils. Disruption of the water table is both a surface- . and an underground- mining problem. Degradation of water quality can result from drain- age from either surface or underground mines. All historical and current data related to stream discharge, water quality, sediment, and biology are available from computer storage through the Nation- al Water Data Storage and Retrieval System (WATSTORE) and through the National Water Data Exchange (NAWDEX). Current data are published in annual Water Resources Data reports for Colora- do and New Mexico.