East of the Continental Divide, glaciation and melt runoff stripped and then crushed and flushed away most of the San Juan Basin's gas and oil shale above the Mancos.
In the Rios Gallina and Chama Watersheds, most Kirtland, Fruitland, and Lewis Shales (and tertiary and confining strata like Pictured Cliffs, Ojo Alamo Sandstones, and the Mesa Verde group) are gone, exposing Mancos Shale.
Mancos Shale, and Elpedro soil derived therefrom, IS the surface of much of these heavily-glaciated Watersheds.
Surface Mancos Shale, Dakota Sandstone and the deep, water-bearing Morrison ARE the locally-significant sources for seasonal and year-round drinking water.