Pennsylvanian-Permian age block faulting has been identified on two regional seismic lines in the Piceance basin. At the south end of a north-south line along the west side of the basin, the Mesozoic section unconformably overlies the Precambrian. Five miles (8 km) to the north, reflectors of the Mississippian Madison Limestone appear in a series of fault blocks downthrown to the north. These faults generally do not displace overlying Mesozoic rocks. In the vicinity of Douglas Creek field, this block faulting created a large horst block on which Madison Limestone is faulted step-wise up the flanks of the structure. The overlying Pennsylvanian Maroon Formation is 50% thinner over the crest of this structure than it is 10 mi (16 km) to the north. Similar features can be see on a second seismic line running east-northeast through the central portion of the basin between DeBeque field and the Grand Hogback. Coming off the ancestral Uncompahgre highland, Madison reflectors appear near the southwest end of the line in a series of fault blocks downdropped to the northeast. Near Rulison field, a large Pennsylvanian-age horst block is present that may have Madison Limestone stripped from its crest. Near the Grand Hogback, Madison Limestone is faulted up to the east to form a Pennsylvanian-age basement high between the Piceance basin and the Eagle basin to the east.

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