Ground-Water Atlas of Colorado Special Publication 53

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• Colorado Geological Survey West Feet 14,000 -1,, Culebra Peak DRAFT East Feet 14,000 12,000 Strati- Unit d 12,000 Era PIP a o graphic 10,000 PlIP t c Hydrologic U 0 T 10,000 (feet) _ TKcp a V c x - 8000 Characteristics E ' L 8000 Silt, sand, and gravels Alluvial aquifer Water -table aquifer of 6000 m $ No ` i Information °M , x '' 6000 4000 Pleistocene Vertical Exaggeration x5 _ _ °'' ' - - 4000 Datum Is sea level EXPLANATION Modified from Geldon, 1989 TKcp; Cuchara and Poison Canyon Formations KJ° Cretaceous (Tertiary and Cretaceous) and Jurassic rocks, undivided Precambrian rocks, undivided Raton and Vermejo Formations and Trinidad M Permian Pennsylvanian Sandstone (Tertiary and Cretaceous) and rocks, undivided Fault - showing movement Figure 6.7 -2. Generalized geologic cross section through the southern Raton Basin. member; a middle member of sandy shale; and an upper member, 100 to 300 feet thick, composed of sandstone, siltstone, and shale that intertongues with the overlying Poison Canyon Formation. The Vermejo and Raton Formations are both coastal -plain deposits. They crop out along the Purgatoire River and its tributaries, and along the eastern portion of the basin. The Tertiary age Poison Canyon Formation is the near - surface formation underlying most of the Park Plateau and the area directly west of Walsenburg. It consists of 2,500 feet of conglomerate and interbedded shale. The overlying Cuchara Formation is 5,000 feet thick, and is composed of red, pink, and white massive sandstone interbedded with shale. HYDROGEOL 0G /C UN /TS The major aquifers in the Raton Basin are the river valley alluvium; the sandstones and siltstones of the Raton, Vermejo, and Trinidad Formations, which are classified as a single aquifer; and the sand- stones and siltstones of the Cuchara and Poison Canyon Formations, which likewise are classified a single aquifer. For administrative purposes, the Colorado Division of Water Resources (DWR) considers the Trinidad Sandstone aquifer as separate from the Raton - Vermejo interval. The Dakota aquifer underlies the entire basin, but it is too deep to be economically developed at present except along the western edge of the basin. As in other parts of the state, the Dakota aquifer's water quality degrades sig- nificantly with increasing depths. The alluvium of the Purgatoire River is discussed as a part of the Arkansas River alluvium in Chapter 5. The physical and hydrologic characteristics of the bedrock aquifers in the Raton Basin are listed in Table 6.7 -1. Cuchara– Poison Canyon Aquifer —The Cuchara and Poison Canyon Formations are hydraulically connected and form the Cuchara - Poison Canyon aquifer. The Poison Canyon contains thicker, more permeable and more numerous sandstone beds than the Cuchara, and is generally a better aquifer. However, where the Cuchara crops out it is often more deeply dissected and contains more s rin s and GROUND -WATER ATLAS OF COLORADO Table 6.7 -I. Hydrogeologic units of the Raton Basin. t, g seeps. (McLaughlin, 1966). The thickness of the Poison Canyon Formation in the northern por- tion of the basin is shown on Figure 6.7 -3. Due to the interbedded nature of this formation, the aquifer is mostly confined. The saturated thickness of the sand- stone and siltstone layers comprising the aquifer is considerably less than the total unit thickness cited in Table 6.7 -1. Raton– Vermejo– Trinidad Aquifer —The Raton Formation consists of a basal sandstone and conglomerate member with some silt- stone, shale, and coal; a middle member of sandy shale with some sandstone and thick, lenticular coal beds; and an upper member composed of sandstone, siltstone, and shale that intertongues with the overlying Poison Canyon Formation. The Vermejo and Raton Formations are both coastal -plain deposits. They crop out along the Purgatoire River and its tributaries, and along the eastern por- tion of the basin. The Raton - Vermejo- Trinidad aquifer in Las Animas County consists of sandstones and coals of the three indi- vidual formations. Total thickness of the Raton - Vermejo- Trinidad aquifer is shown on Figure 6.7 -4, and the thickness of the sand- SP 53 Strati- Unit Era System Series graphic Thickness Physical Hydrogeologic Hydrologic Unit (feet) Characteristics Unit Characteristics Quaternary Holocene Alluvium Silt, sand, and gravels Alluvial aquifer Water -table aquifer of limited extent Pleistocene Devil's Hole Formation Oligocene Farisita Conglomerate oIntrusive Granitic to gabbroic igneous rocks stocks, dikes, and sills U Tertiary Huerfano 2,000 Variegated shale and Formation limestone Eocene Cuchara 5,000 Pink and white sand - _ Target formation for Formation stone with shale # _ PDlsa coalbed methane;trans- Poison Tan, gray and olive uchara canyon missivities of 0.20 -575 Paleocene Canyon 2,500 sandstone, conglomerate ' -' ft /day; yields 0.07 -33 Formation and shale v~ gpm Raton Formation 1,000- 1,600 Gray, green, and black° shale, siltstone with sandstone, coal ` Rafon Vermeto Transmissivities of 0.02 -79 ft2 /day; yields Vermejo 80 -550 Gray, green, and black Formation shale, siltstone with rmdadraqulfe' 0.04 -16 gpm sandstone, coal Trinidad 45-310 Tan and gray sandstone Sandstone with shale partings. Pierre Shale 1,600- Shale, with interbedded sandstone in the upper = Confining jayer Sandstone la ht layers might o Upper 2,300 100 -300 feet ti : ?= yield f ` limited water Cretaceous Cretaceous Niobrara Formation 450 -570 Chalky and sandy shale with limestone in lower Ft. Ft. Hayes Hayes Limestone Member supplies wells in 50 -70 feet Limestone Member adjacent areas Carfile Shale 225 -290 Sandstone in upper 5 -30 feet, shale below Codell Sandstone Codell Member Sandstone supplies wells in Member adjacent areas Greenhorn 25 -35 Thin gray limestone Yields small quantifies of Limestone interbedded with shale water to wells in adjacent areas raneros Shale 185 -235 Shale and limestoneCshfintrJ _ 15e Not an aquifer in Raton Basin Lower Dakota White and tan _... _ MOC Average porosity range Cretaceous Sandstone 50 -200 sandstone Dakota aqutfe = 10 -20 %; average hydraulic conductivity 0.2 ff/day t, g seeps. (McLaughlin, 1966). The thickness of the Poison Canyon Formation in the northern por- tion of the basin is shown on Figure 6.7 -3. Due to the interbedded nature of this formation, the aquifer is mostly confined. The saturated thickness of the sand- stone and siltstone layers comprising the aquifer is considerably less than the total unit thickness cited in Table 6.7 -1. Raton– Vermejo– Trinidad Aquifer —The Raton Formation consists of a basal sandstone and conglomerate member with some silt- stone, shale, and coal; a middle member of sandy shale with some sandstone and thick, lenticular coal beds; and an upper member composed of sandstone, siltstone, and shale that intertongues with the overlying Poison Canyon Formation. The Vermejo and Raton Formations are both coastal -plain deposits. They crop out along the Purgatoire River and its tributaries, and along the eastern por- tion of the basin. The Raton - Vermejo- Trinidad aquifer in Las Animas County consists of sandstones and coals of the three indi- vidual formations. Total thickness of the Raton - Vermejo- Trinidad aquifer is shown on Figure 6.7 -4, and the thickness of the sand- SP 53