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• conditions or "native" transmissivities. In some areas, old uncaved workings appear to serve as open conduits for groundwater transport. Hydrological data indicate that old workings have had a profound effect on the present groundwater regime within the mine plan area. 2.04.6 Geology Description The coal which was to be mined by the proposed operations is located in the northern extent of the Trinidad-Raton Basin, approximately 4 miles northwest of Walsenburg, Colorado. As an "old coal field", the geology of the Trinidad-Raton Basin has been thoroughly studied and many reports on the area have been published. The U.S. Geological Survey published a summary report of the area of immediate interest: "Geology and Coal Resources of the Walsenburg Area, Huerfano County, Colorado", by R. B. Johnson, 1958 (U.S.G.S. Bulletin 1042-0). Amore exhaustive and more recent treatment of the entire basin is found in an unpublished report, "Regional Coal Resources Study of the Trinidad-Raton Basin, Colorado and New Mexico", by Amuedo and Ivey, Engineering Geologists, Denver, Colorado, 1974. The general geology in the permit area and adjacent areas is illustrated in Figure 2, Geologic Structural Setting, and Figure 3, General Stratigraphic Column. The upper formation is the Poison Canyon of Tertiary Age, consisting of a series of sandstones and sandy shales which are as much as 2500 feet thick. It also contains thin beds of yellow shales and conglomer- ates. The Poison Canyon rests unconformably upon lower formations. • Underlying the Poison Canyon is the Raton Formation, probably of late Cretaceous age. In the permit area and adjacent areas, the Raton is perhaps only ten feet thick, and may be nonexistent inasmuch as it closely resembles the underlying Vermejo formation. In the permit area, the Raton formation is of no economic importance. However, it thickens dramatically towards the south and becomes the dominant coal formation near the towns of Trinidad, Colorado and Raton, New Mexico. The underlying Vermejo formation, which is of Cretaceous age, is the important coal bearing unit in the permit area. This formation consists of sandstones, siltstones, shales, carbona- ceous and silty shales, and numerous lenticular coal beds interbedded with sandstone, siltstone and shale. The Vermejo formation thickens from south to north and is approxi- mately 400 feet thick in the Walsenburg area. In this area, the Veremjo formation may contain up to eight coal beds of irregular thickness and extent. There are some six coal seams in the Walsenburg area that have been previously mined and are generally greater than three feet in thickness. Underlying the Vermejo formation is the Trinidad sandstone, also of Cretaceous age, which is covered by recent colluvium in the mine plan and adjacent area. While the contact between the Trinidad and the Verntejo is not certain throughout the mine plan area, its projected location is shown on Figure 2, Geologic Structural Setting. 2.04-8