boulder_field Published October 3, 2016 at 1800 × 1066 in Tertiary Paleovalleys in the Laramie Mountains, Wyoming Large boulders occur at the base of White River Formation in the Toltec Tertiary paleovalley. The Toltec paleovalley is on the west side of the Laramie Mountains where basal Tertiary strata are exposed at and close to the range margins.