The Pieance Creek basin encompasses nearly 4,000 sq mi, including parts of Delta, Garfield, Gunnison, Mesa Moffat, Pitkin and Rio Blanco Counties. The basin is strongly asymmetric, with moderately gentle west and southwest flanks and steeply dipping east and northeast flanks f()filled by the Grand Hog. back monoclime. The axis of the basin parallels the Grand Hogback in the central part of the basin and is bifurcated in the southern and northern parts by basinward-plunging anticlines. The basin contains a maximum of about 27;000 ft of sedimentary and this figure represents maximum structural relief on the Precambrian between the lowest point in the basin and the highest points on the White River and Uncompahgre uplifts.