The Robinson Limestone Member is one of eight carbonate members of the 5,000 ft thick, predominantly sandstone, Minturn Formation (Desmoinesian) in the study area west of the Gore Range in Central Colorado. The Robinson Limestone Member consists of three limestone units (lower, middle, and upper) interstratified with marine and nonmarine sandstone beds. Total thickness of the Robinson ranges from 200 to 400 ft.

The areal distribution and the thicknesses of four time-transgressive facies which make up each of the Robinson limestone units imply an asymmetrical deposition basin with a relatively deep marginal trough along the east side.

From east to west the facies are (1) an oolite facies composed of superficial oolites, pseudo-oolites and oncolites in micro-spar or micrite; it is interpreted to be a shallow-water, high-energy deposit on the east edge of the marginal trough; (2) a tubular foraminiferal facies composed mainly of tubular Foraminifera micrite; (3) a phylloid algae facies of biomicrite containing abundant Archaeolithophyllum, Eugonophyllum, fusulinids, and Komia; the phylloid algae facies is interpreted to be a deeper water deposit near the middle of the trough; (4) a stromatolite facies of stromatolites, laminated micrite, and vuggy ostracod-bearing intramicrudite, which indicate quiet-water deposition near the western margin of the trough. The overall patterns of the limestone facies and sandstone bed indicate intervals of rapid marine transgression followed by relatively slow depositional regression.

Bioherms as thick as 80 ft are in the areas of phylloid algae and stromatolite facies. Nonphylloid algae appear to be the major components of these bioherms. However, recrystallization and dolomitization make recognition of the algae types difficult.

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