The actinopterygian fishes "Leptolepis" schoewei and "Pholidophorus" americanus occur north of Canon City in the basal part of the Ralston Creek Formation. The same fish association of the "Ralston Creek Formation" of Colorado, in the Todilto Formation of New Mexico, in the Hulett Sandstone Member of the Sundance Formation in northwestern Wyoming and southern Montana, and the Stockage Beaver Shale Member and Canyon Spring Sandstone Member of the Sundance in northeastern Wyoming and western South Dakota indicates the same time interval. Based on the occurrence of Kepplerites macleani in the Hulett Sandstone Member, all the fish horizons of these units are placed in the lower Callovian, Middle Jurassic.--Journal abstract.

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