occurs below Bruin Point, Utah in the Green River Formation (Eocene) due to canyon erosion, thereby allowing the volatile compounds to freely migrate to the surface with only bitumen remaining in the sandstone.
View toward the west from Bruin Point, Utah (10,131 feet (3,088 meters)) into Water Canyon. The access road is exceptionally steep and requires a high clearance vehicle.
Block of asphaltic sandstone from the Green River Formation that was quarried below Bruin Point in the early 1800s.
Gravity-powered aerial tramway relic below Bruin Point, circa 1920s.
Here’s a link for geo-nerds: Sunnyside bitumen-impregnated sandstone reservoirs at Bruin Point, southwest Uinta Basin, Utah.