sporadic pulses of mud swept southward into the Death Valley region during the erosion of highlands in north-central Nevada. 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. All told, these eight formations and one group are thick and are buried below much of the Cottonwood, Funeral, Grapevine, and Panamint ranges. Good outcrops can be seen in the southern Funeral Mountains outside the park and in Butte Valley within park borders. The Eureka Quartzite appears as a relatively thin, nearly white band with the grayish Pogonip Group below and the almost black Ely Springs Dolomite above. All strata are often vertically displaced by normal faulting. Change to active margin and uplift The western edge of the North American continent was later pushed against the oceanic plate under the adjacent ocean. An area of great compression called a subduction zone was formed in the early-to-mid Mesozoic, which replaced the quiet, sea-covered continental margin with erupting volcanoes and uplifting mountains. A chain of volcanoes pushed through the continental crust parallel to the deep trench, fed by magma rising from the subducting oceanic plate as it entered the Earth's hot interior. Thousands of feet (hundreds of meters) of lavas erupted, pushing the ocean over to the west. Compressive forces built up along the entire length of the broad continental shelf. The Sierran Arc, also called the Cordilleran Mesozoic magmatic arc, started to form from heat and pressure generated from the subduction. Compressive forces caused thrust faults to develop and granitic blobs of magma called plutons to rise in the Death Valley region and beyond, most notably creating the Sierra Nevada Batholith to the west. Thrust faulting was so severe that the continental shelf was shortened and some parts of older formations were moved on top of younger rock units. The plutons in the park are Jurassic and Cretaceous aged and are located toward the park's western margin