Iight-banded lower slopes of Pyramid Peak and the gorges of Titus and Grotto Canyons. Although details of geography varied during this immense interval of time, a north northeasterly trending coastline generally ran from Arizona up through Utah. A marine carbonate platform only tens of feet deep but more than 100 miles wide stretched westward to a fringing rim of offshore reefs. Down gentle slopes to the west of such rims of reefs, limy mud and sand eroded by storm waves from the reefs and platform collected on the quieter ocean floor at depths of 100 feet or so. The extent and stability of this great shallow carbonate-rich sea are not matched in today's restless world.
Caribbean analogs are tiny by comparison.
The carbonate uniformity was seriously interrupted only twice. This great white band of Ordovician rock stands out on the summit of Pyramid Peak, widely near the Racetrack, and high on the east shoulder of Tucki Mountain. No American source is known for the Eureka sand, which once blanketed a 150,000 square-mile belt from California to Alberta. It may have been swept southward by longshore currents from an eroding sandstone terrain in Canada, but the origin of both the Eureka and contemporaneous sands blanketing much of the Midwest remains shrouded in mystery. Between 350 and 250 million years ago sporadic pulses of mud swept southward into the Death Valley region during the erosion of highlands in north-central Nevada.