Perhaps the richest producer of Miocene-age (22-to-5-million-year-old) plants in the entire state of Nevada is a geologic rock deposit known as the Middlegate Formation. It is exposed primarily in the Middlegate Hills a number of miles from Fallon. In this area some 64 species of fossil plants have been described, including such diverse types as evergreen live oak, giant sequoia, willow, fir, maple and spruce. The fossil specimens, which consist of leaves, winged seeds (called samaras in technical botanical terminology), acorn cups, seed pods and branchlets, occur as pale to dark brown carbonized impressions on a cream-white to pale-brownish matrix of opaline shale–many of them exhibiting such an exceptional degree of preservation that the original delicate venation on the leaves is clearly visible.
All of the remains are Middle Miocene in geologic age, dated by radiometric methods at some 16 million years old. They occur in the uppermost (the youngest layers of deposition) 30 feet of the Middlegate Formation, just below the overlying Middle Miocene Monarch Mill Formation, whose basal sedimentary conglomerates have yielded to paleontologists a large vertebrate fauna, including the silicified bones of moles, rabbits, squirrels, beavers, mountain beavers, mice, weasels, martins, rhinocetotids, oreodonts, camels, llamas and pronghorns
Such scientifically invaluable fossil vertebrate material on Public Lands is of course off limits to all collectors who do not possess a special use permit issued by the Bureau of Land Management, a formal collecting status that is perhaps well understood by most amateurs and professional paleontologists alike. At present, there is no such legal restriction on the hobby gathering of leaves, winged seeds, and other paleobotanical remains at Middlegate–but that, too, could change.
The troubling circumstance is that commercial collecting interests have recently begun to concentrate on a select number of fossil leaf-yielding fields in Nevada–obviously those sites which happen to provide them with the greatest numbers of well-preserved specimens. This is patently illegal activity, since no fossil remains collected on Public Lands may be either sold or bartered. And while there is certainly nothing criminal about selling fossil specimens collected on private lands (with the land owner’s unambiguous permission, of course), any desecration of a fossil horizon on Public Lands in an attempt to secure as many saleable remains as possible is without question an offense punishable by law. Also, such behavior is with sure consequence horribly counterproductive, since it only invites officials with the Bureau of Land Management and the Forest Service to close down popular fossil areas, preventing conscientious amateurs from sampling places of significant paleontological interest.
The most efficient way to locate fossil plants in the Middlegate Hills is to dig into the slabby-weathering siliceous shales, exposing fresh sedimentary strata below the surface. Fortunately, most of the shales within a few inches of the surface are severely fractured; hence, little splitting of them is necessary, since they tend to separate from the outcrops in thin sheet-like plates. Watch for the fossil plant compressions and impressions along the bedding planes of every shale fragment you remove from the hillside exposures. The deeper you dig, though, the more thickly bedded the opaline shales become, until at last it will become necessary to begin splitting the extremely dense, concrete-like rocks. When doing this, always remember to wear safety goggles, or at least some kind of eye protection such as sunglasses. The denser, thick-bedded opaline strata crack apart only with the greatest of applied brute force, thus increasing the likelihood that sharp fragments might launch off the matrix into your eyes. Stand slabs of shale on end, then give them a sure whack with the blunt end of a geology hammer. If you’re fortunate, the sedimentary layers will break apart along their original planes of deposition, revealing perfect carbonized leaf and seed impressions and compressions to their first light of day in approximately 16 million years.