lowlands and a wide, shallow shelf but no volcanoes, lay to the east near where Las Vegas now resides. The first formation to be deposited in this setting was the Noonday Dolomite, which was formed from an algal mat-covered carbonate bank. Today it is up to thick and is a pale yellowish-gray cliff-former. The area subsided as the continental crust thinned and the new ocean widened; the carbonate bank soon became covered by thin beds of silt and layers of lime-rich ooze. These sediments in time hardened to become the siltstone and limestone of the Ibex Formation. A good outcrop of both the Noonday and overlying Ibex formations can be seen just east of the Ashford Mill Site. An angular unconformity truncates progressively older (lower) parts of the underlying Pahrump Group starting in the southern part of the area and moving north. At its northernmost extent, the unconformity in fact removed all of the Pahrump, and the Noonday rests directly on the Proterozoic Complex. An ancient period of erosion removed that part of the Pahrump due to its being higher (and thus more exposed) than the rest of the formation. Passive margin formed As the incipient ocean widened in the Late Proterozoic and Early Paleozoic, it broke the continental crust in two and a true ocean basin developed to the west. All the earlier formations were thus dissected along a steep front on the two halves of the previous continent. A wedge of clastic sediment then started to accumulate at the base of the two underwater precipices, starting the formation of opposing continental shelves. Three formations developed from sediment that accumulated on the wedge. They are, from oldest to youngest: Johnnie Formation (varicolored shaly), Stirling Quartzite, Wood Canyon Formation, and the Zabriskie Quartzite. Together the Stirling, Wood Canyon, and Zabriskie units are about thick and are made of well-cemented sandstones and conglomerates. They also contain the region's first known fossils of complex life: Ediacara fauna, trilobites, archaeocyathas, and primitive echinoderm burrows have been found in the Wood Canyon Formation. The very earliest animals are exceedingly rare, occurring well west of Death Valley in lime-rich offshore muds contemporary to the Stirling Quartzite. Good outcrops of these formations are exposed on the north face of Tucki Mountain in the northern Panamint Mountains. The side road to Aguereberry Point successively traverses the shaly Johnnie Formation, the white Stirling Quartzite, and dark quartzites of