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 wide stretched westward to a fringing rim of offshore reefs. Lime-rich mud and sand eroded by storm waves from the reefs and the platform collected on the quieter ocean floor at depths of or so. The Death Valley area's carbonates appear to represent all three environments (down-slope basin, reef, and back-reef platform) owing to movement through time of the reef-line itself.