Landform development of City of Rocks State Park and Giant of the Mimbres
— Jerry E. Mueller and C. R. Twidale

Bedrock landforms at City of Rocks State Park and Giant of the Mimbres are developed in the lowermost ash-flow tuff unit of the Sugarlump Rhyolite. Convex-upward sheeting fractures and an orthogonal fracture set in the ignimbrite sheet have been exploited by weathering and erosion to produce a landscape of pinnacles, boulders, balanced rocks, clefts or corridors and rock platforms. Flared sidewalls on the pinnacles and the presence of rock basins and stains on the platforms indicate that the bedrock landforms are of etch origin. Etch forms develop beneath a soil mantle at the weathering front, but are subsequently exposed as the overlying regolithic cover is stripped. The occurrence of multiple flares on some pinnacles suggests that several episodes of alternate weathering and erosion were required to produce the modern landscape.