While beneath inland seas, what became the Rio Chama Watershed amassed layers of sedimentary rock.
Glaciation and erosion, flumed southwards by the Continental Divide (west) and the volcanically-inspired uplift (east), exposed Cretaceous sedimentary rocks.
Extreme weights of glaciation probably contributed to flexure, faulting, fracturing, and flushing by compressing and decompressing any remaining formations as the glacial melt flushed the Watershed.
Mancos shale, here, produces drinking water, so shallow wells pose additional risks for ANY fracking operations.