In Search of Vanished Ages--Field Trips to Fossil Localities in California, Nevada, and Utah
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i In Search Of Vanished Ages Field trips to fossil localities in California, Nevada, and Utah By Inyo A view across the middle Miocene Barstow Formation on California’s Mojave Desert. Here, limestone concretions that occur in rocks deposited in a freshwater lake system approximately 17 million year-ago produce exquisitely preserved, fully three-dimensional insects, spiders, water mites, and fairy shrimp that can be dissolved free of their stone encasings with a diluted acid solution—one of only a handful of localities worldwide where fossil insects can be removed successfully from their matrixes without obliterating the specimens. ii Table of Contents Chapter Page 1—Fossil Plants At Aldrich Hill 1 2—A Visit To Ammonite Canyon, Nevada 6 3—Fossil Insects And Vertebrates On The Mojave Desert, California 15 4—Fossil Plants At Buffalo Canyon, Nevada 45 5--Ordovician Fossils At The Great Beatty Mudmound, Nevada 50 6--Fossil Plants And Insects At Bull Run, Nevada 58 7-- Field Trip To The Copper Basin Fossil Flora, Nevada 65 8--Trilobites In The Nopah Range, Inyo County, California 70 9--Field Trip To A Vertebrate Fossil Locality In The Coso Range, California 76 10--Plant Fossils In The Dead Camel Range, Nevada 83 11-- A Visit To The Early Cambrian Waucoba Spring Geologic Section, California 88 12-- Fossils In Millard County, Utah 95 13--A Visit To Fossil Valley, Great Basin Desert, Nevada 107 14--High Inyo Mountains Fossils, California 119 15--Early Cambrian Fossils In Western Nevada 126 16--Field Trip To The Kettleman Hills Fossil District, California 130 17--Trilobites In The Marble Mountains, Mojave Desert, California 135 18--Late Triassic Ichthyosaurs And Invertebrate Fossils In Nevada 143 19--Field Trip To Pleistocene Lake Manix, Mojave Desert, California 157 20--Paleozoic Fossils At Mazourka Canyon, Inyo County, California 164 21--Fossil Leaves And Seeds In West-Central Nevada 172 iii 22--A Visit To The Sharktooth Hill Bone Bed, Southern California 178 23—Dinosaur-Age Fossil Leaves At Del Puerto Canyon, California 188 24--Early Triassic Ammonoids In Nevada 194 25—Fossil Plants At The Chalk Bluff Hydraulic Gold Mine, California 198 26--In Search Of Fossils In The Tin Mountain Limestone, California 210 27—High Sierra Nevada Fossil Plants, Alpine County, California 220 28--Ordovician Fossils In The Toquima Range, Nevada 230 29—Late Miocene Leaves At Verdi, Washoe County, Nevada 236 30--A Visit To The Fossil Beds At Union Wash, California 242 31—Ice Age Fossils At Santa Barbara, California 246 32--Early Cambrian Fossils Of Westgard Pass, California 254 On-Site Images and Photographs of Fossils From Each Field Trip 262 Geologic Time Scale 297 iv Dedicated to my parents who introduced me to the glories of nature 1 Chapter 1 Fossil Plants At Aldrich Hill, Nevada The Great Basin wilds of west-central Nevada are rich in productive fossil plant localities. While they are probably not as well known to amateur fossil plant hunters as the classic Paleocene through Late Miocene (roughly 64 to 5.3 million years ago) leaf-bearing sites of Oregon, Idaho, Washington, Montana, Colorado and Wyoming, the Nevada fossil plant deposits continue to yield many excellently preserved paleobotanical remains. One of the more interesting and paleontologically rewarding leaf and seed-yielding areas lies near Yerington (the county seat of Lyon County) at Aldrich Hill. Here can be collected some 35 species of ancient plants from what geologists call the middle Miocene Aldrich Station Formation, a geologic rock unit dated at roughly 13 to 12.5 million years old. Among the many fossil plant remains found at Aldrich Hill are complete, carbonized leaves from an evergreen live oak, in addition to many conifer winged seeds and even giant sequoia foliage. It is indeed a special place to visit, an isolated region in the Great Basin "outback" where the Bureau of Land Management still permits the hobby collecting of fossil plant remains--a situation that could change literally overnight, by the way, should commercial collecting interests begin to raid the stratigraphic section, desecrating the integrity of the exposures and destroying in the process the great scientific value of the locality. Fortunately, Aldrich Hill remains accessible to the general public, and folks interested in collecting fossil plants there for personal use only may continue to visit, remembering of course that such specimens gathered must be neither sold nor bartered--activities which would constitute a clear violation of the rules and regulations established by the Bureau of Land Management for visitors to America's public lands. All of the fossil plants--including evergreen live oak leaves, spruce winged seeds, conifer needles, alder cones, and giant sequoia/big tree foliage--occur in the tan to reddish-brown and cream-colored diatomaceous to tuffaceous mudstones and shales of the middle Miocene Aldrich Station Formation exposed on the north side of Aldrich Hill. Excellent outcrops of the plant-bearing strata can be examined along the main wash which trends generally east-west across the northern side of Aldrich Hill. Additional productive fossiliferous exposures can be found in the minor erosion gullies that dissect the north slope of the hill. It should also be pointed out that virtually every outcrop of diatomaceous mudstones and shales in the Aldrich Hill district yields fossil plant material in varying degrees of relative abundance, from very rare to common, although the prominent and accessible exposures along the north side of the hill have in a historical sense provided collectors with the majority of paleobotanical remains. 2 When fossil hunting at Aldrich Hill, as at most other fossil leaf and seed-yielding localities, try to cover as much terrain as possible in search of the most productive layers. Split heaps of the shales with the blunt end of a geology hammer whenever you stop for a "look-see." Some folks prefer to use the pick end of a geology rock hammer, though this technique actually decreases the likelihood of splitting with precision the blocky diatomaceous mudstones and shales; too, a number of collectors prefer a roofer's or brick-layer's-style hammer, with a wide narrow blade, which theoretically splits shales with great effectiveness. Such a hammer probably works well with very soft, classically fissile shales, but the tool lacks any kind of "punch," or heft, for cleaving bulkier and more compacted mudstones and shales. The upshot: the blunt end of a traditional geology hammer splits the Aldrich Station Formation diatomaceous shales and mudstones quite nicely. Remember, of course, to wear safety goggles, or some manner of eye protection while splitting the mudstones and shales. Although nowhere abundant, the fossil plant impressions in the Aldrich Station Formation are nevertheless common and even obvious at several horizons in the diatomaceous material. Watch for their pale to dark-brown, carbonized coloration on the tan to reddish-brown and cream-colored rocks. Associated with the leaves, winged seeds, and twigs are conspicuous oval specimens roughly one-half to one inch in diameter. These fossils represent the internal molds of fresh water clam shells; the actual shell substance has long since been dissolved away, as the siliceous mudstones and shales were evidently a poor medium of preservation for the tests of pelecypods. If a microscope is available, you can, in addition to finding the plants and clams, examine the remains of an especially prolific fossil type at Aldrich Hill--the diatom. This is a microscopic photosynthesizing single-celled plant which during the geologic past contributed its resistant siliceous remains in vast numbers to the plethora of paleohistory in the rocks, particularly in west-central Nevada in rocks of Middle through Late Miocene age (roughly 17 to 5 million years ago). The scientific extraction of diatoms for paleobotanical study is a dangerous operation, involving as it does the use of several powerful acids, among them hydrochloric, sulfuric and hydrofluoric--potent brews that if not handled properly can cause frightful or even life-threatening burns. It is a process only an expert should attempt. Fortunately, though, you can get an adequate and general view of diatoms simply by powdering a small amount of diatomaceous matrix on a glass microscope slide and then examining the residues under moderate to high powers of magnification. Most of the diatoms from the Aldrich Hill district resemble minute boxcars and discs. Excluding the numerous species of diatoms identified from the Aldrich Station Formation, some 35 species of fossil plants have been described from the exposures at Aldrich Hill--a fossil deposit first investigated scientifically in the early 1940s by the late paleobotanist 3 Daniel I. Axelrod during one of his geological reconnaissance investigations in Nevada. Axelrod eventually published his paleobotanical, paleoecological, and geological conclusions concerning the Aldrich Hill paleoflora in a monumental paleobotanical monograph, where he additionally describes in detailed scientific fashion three more important Nevada fossil floras (Middlegate Formation, Chloropagus Formation, and Desert Peak Formation). All of the fossils from Aldrich Hill occur in the Aldrich Station Formation, as named by Axelrod in his treatise, a geologic rock unit originally considered transitional Miocene-Pliocene (about 10 million years old by the geologic time scale then in fashion--as recalibrated, the Miocene- Pliocene is now established