The Death Valley depression harbors the lowest point in the United States (approximately 260 feet below sea level) and stretches roughly 120 miles in a northwest-southeast direction. Its northernmost basin is bounded by the Last Chance Range to the west and the Grapevine Mountains to the east. As one travels southward, the Cottonwood Mountains and Panamint Range rise up on the west side of the valley, while to the east the forbidding Funeral Range looms. Further south, the Amargosa Range and Black Mountains form the east boundary of the valley, while the ramparts of the Panamint Range make up the west boundary. The southernmost basins of the Death Valley depression are bounded by the Owlshead Mountains and Avawatz Mountains (to the east and northeast, respectively). The southern terminus of the valley is the Salt Spring Hills (home of the famous Amargosa Mine). The basin extending southeast of the Salt Spring Hills becomes the Silurian Valley.
The mountains bounding the northernmost basin of the Death Valley depression (the Last Chance Range and Grapevine Mountains) are mostly composed of Paleozoic marine sedimentary rocks. The Panamint Range is comprised of much older rocks. The Panamints are an uplifted block of ancient Precambrian to Cambrian metamorphic and sedimentary rocks intruded by younger Mesozoic granites. The largest Mesozoic intrusion occurs in the northernmost part of the range, near Grapevine Canyon and Ubehebe Peak. The intrusion is batholithic in size with a total outcrop area of roughly 200 square miles. Smaller Mesozoic plutons occur near Harrisburg and Skidoo, near Panamint City (in the central part of the range), and further south, on Manly Peak. The southernmost part of the Panamints is overlain by younger Tertiary-age volcanics.
The Funeral Mountains are an uplifted, block-faulted wedge of Precambrian to early Paleozoic sediments and metasediments. The Paleozoic sediments range in age from early Cambrian to early Devonian and represent a virtually complete record of early Paleozoic history.
The Black Mountains are a northwest-southeast trending block of ancient basement rock wedged between the Death Valley Fault Zone and the Furnace Creek Fault Zone. This tectonic wedge is block-faulted upward and consists of Precambrian to Cambrian metamorphic and sedimentary rocks intruded and overlain by younger Mesozoic granite plutons and younger still Tertiary volcanic rocks. The Tertiary volcanics crop out mostly on the east flank of the Black Mountains and consist of basalts, rhyolites, and pyroclastics. The largest deposit of pyroclastic rock is 500 feet thick and consists of a tuff-breccia. These pyroclastics rocks are testament to the violent history of this part of the Black Mountains.
The southernmost portion of the Black Mountains, the Ibex Hills, and the Saddle Peak Hills all consist of ancient Precambrian to Cambrian metamorphic and sedimentary basement rocks. To the west, across Death Valley, the Owlshead Mountains present a granitic front. The Owlshead Mountains are mostly composed of Mesozoic granite, although much younger Quaternary-Tertiary volcanics occur in the northern part of the range.
To the southeast of the Owlshead Mountains lie the Avawatz Mountains. This uplifted block of Precambrian metamorphic basement rock is intruded by small Mesozoic granitic stocks and forms the locus of several major fault zones. The Death Valley Fault Zone, the Mule Spring Fault, and the Arrastre Spring Fault all meet in the Avawatz Mountains.
The area of interest for the Lost Breyfogle Mine encompasses a vast area which includes the Funeral Mountains and the surrounding country extending even into Nevada. Indeed, tantalizing evidence for the Lost Breyfogle was discovered in a canyon east of Beatty, Nevada. During the 1930's, a prospector stumbled on a rock formation with an old inscription carved on it. The engraving read: "BY. FOGLE 1863". But most accounts place Breyfogle's discovery somewhere in the Death Valley country. To start with, prospectors may
want to concentrate on the Funeral Mountains, in particular the central and western portions of the range. Since the area is so extensive, a careful survey of the many canyons that drain the western flank of the Funerals may prove to be fruitful. A metal-detector would certainly be useful in the search. Prospectors must realize that a good portion of the area of interest lies within Death Valley National Park. Some restrictions on prospecting may exist.