Geodiversity Atlas—Mojave Desert I&M Network Index

The oldest Paleogene units in the MOJN include the late Eocene through early Oligocene Titus Canyon Formation at DEVA. At GRBA igneous dikes, sills and a biotite granite are referenced to be either Eocene or Oligocene in age. Additionally, rhyodacite flows and subvolcanic intrusive rocks at GRBA are reported to date to the early Oligocene. The Ubehebe Formation in DEVA spans from the late Oligocene to the early Miocene. Additionally, the Rainbow Gardens Formation in PARA is a late Oligocene to early Miocene unit.

The Miocene, especially the late Miocene, is well represented by rock units in the MOJN parks. The oldest known Miocene unit is the Horse Spring Formation at LAKE which spans the early to middle Miocene with several members. Early Miocene tuffs and unnamed sedimentary rocks are also found at MOJA. During the middle to late Miocene there was both extrusive and intrusive igneous activity as evidenced by rocks exposed within CAMO, LAKE, MOJA and PARA. A number of middle to late Miocene formations are mapped in DEVA including the Artist Drive, Eagle Mountain, and Furnace Creek Formations. The Hualapai Limestone and Muddy Creek Formation are mapped in LAKE. Additionally, the “Rocks of the Overton Arm” and the “Rocks of the Grand Wash Trough” span the middle and late Miocene at LAKE. The “Rocks of the Grand Wash Trough” also occur at PARA. The Cima volcanic field at MOJA became active during the late Miocene.

Pliocene rocks include a number of named formations in DEVA including the Greenwater Volcanics, Copper Canyon Formation, and Funeral Formation, along with a variety of volcanic units. At LAKE the Pliocene is represented by the Bouse Formation, along with the “Deposits of Hualapai Wash” and Deposits at Jumbo Pass”. A number of unnamed Pliocene units occur in MOJN parks.

The oldest Mesozoic unit known in the MOJN parks is the Early–Middle Triassic Moenkopi Formation which is mapped in LAKE, MOJA and PARA. Unnamed Middle Triassic intrusive igneous rocks occur at JOTR. The Late Triassic Chinle Formation is exposed in LAKE and PARA.

The Butte Valley Formation at DEVA is an Early Jurassic marine unit. The Early Jurassic Moenave and Kayenta Formations are mapped in LAKE and PARA. The Early Jurassic Aztec Sandstone is mapped in two of the MOJN parks, LAKE and MOJA, while the time-equivalent Navajo Sandstone is mapped in PARA, the Colorado Plateau park. A variety of Jurassic intrusive rocks occur within GRBA, JOTR, and MOJA. 6 The McCoy Mountains Formation is a possible Early Cretaceous unit in JOTR. Late Cretaceous igneous rocks, both intrusive and extrusive, are mapped at DEVA, GRBA, JOTR, LAKE, and MOJA.

The Paleozoic is well represented throughout the parks of the MOJN. The transition between Proterozoic and early Cambrian is preserved in several parks of the network. The Cambrian marks a worldwide event in the history of life referred to as the “Cambrian Explosion”. This transition is marked by an abundant fossil record preserved with the first organisms incorporating calcium carbonate exoskeletons. The Waucoban Series in DEVA was studied and defined by paleontologist Charles Walcott during the late 1890s, and is the reference section for this earliest Cambrian diversification of life. A large number of early Cambrian units are mapped in DEVA, including the Wood Canyon Formation, Zabriskie Quartzite, Poleta Formation, and other units. The Wood Canyon Formation and Zabriskie Quartzite are also mapped in MOJA, along with the Latham Shale and other early Cambrian units. The Prospect Mountain Quartzite marks the Proterozoic–Cambrian transition at GRBA.

The early–middle Cambrian is preserved by the Tapeats Sandstone in LAKE. The middle Cambrian Bright Angel Shale and Muav Limestone are mapped in both LAKE and PARA. At DEVA, the middle Cambrian is represented by the Carrara and Bonanza King Formations. The Bonanza King Formation is also present in MOJA. The late Cambrian Nopah Formation is exposed in DEVA and 5 MOJA. At GRBA the late Cambrian is represented by several formations including the House Limestone which spans into the Early Ordovician.

At DEVA, GRBA, and LAKE the Early and Middle Ordovician are recorded in the Pogonip Group. The Eureka Quartzite dates to the Late Ordovician at DEVA and GRBA.

The Silurian is documented in the Ely Springs Dolomite and Hidden Valley Dolomite within DEVA. There are also some unnamed Silurian rocks on Bullfrog Mountain in DEVA.

The Hidden Valley Formation extends into the Early Devonian in DEVA. The Lost Burro Formation spans the Early to Late Devonian at DEVA. The Early Devonian at GRBA is marked by the Sevy Dolomite, overlain by the Simonson Dolomite and Guilmette Formation. Middle to Late Devonian units include the Sultan Formation, mapped in western LAKE and MOJA, and the Temple Butte Formation, mapped in eastern LAKE and PARA.

Mississippian-age rocks are preserved in DEVA, LAKE, MOJA and PARA. The Early Mississippian is mapped in DEVA with the Tin Mountain Limestone. The Early–Middle Redwall Limestone occurs within LAKE and PARA. At MOJA the Monte Cristo Formation represents the Early–Middle Mississippian. The Perdido Group, Learning Rock Formation and Mexican Spring Formation mark the Early and Middle Mississippian in DEVA, and the Rest Spring Shale and Indian Springs Formation mark the Late Mississippian. At LAKE and PARA several Late Mississippian formations of the Supai Group are mapped and extend into the Pennsylvanian. The Pennsylvanian at DEVA and MOJA is represented by the Bird Spring Formation.

The early Permian is exposed in four MOJN parks: DEVA, LAKE, MOJA, and PARA. The Bird Spring Formation spans from the Pennsylvanian into the early Permian in DEVA and MOJA. The Keeler Canyon Formation also extends from the Pennsylvanian into the Permian at DEVA. Additional early Permian units at DEVA include the Osborne Canyon Formation, Darwin Canyon Formation, Lone Pine Formation, Upland Valley Limestone, and Owens Valley Group. At LAKE and PARA the early Permian is represented by the Pakoon Limestone, Esplanade Sandstone, Hermit Shale, Coconino Sandstone, Toroweap Formation, and Kaibab Limestone.

Rocks of Precambrian age (in the informal sense of “older than the Cambrian”) are well exposed and documented within several parks of the MOJN and span much of the Proterozoic Eon. Paleoproterozoic and Mesoproterozoic igneous and metamorphic rocks occur at CAMO, DEVA, JOTR, LAKE and MOJA. The Neoproterozoic is represented in DEVA, from oldest to youngest, by the Pahrump Group, Johnnie Formation, Sterling Quartzite and the lower portion of the Wood Canyon Formation. At GRBA the Neoproterozoic units include the McCoy Creek Group and the lower portion of the Prospect Mountain Quartzite. At MOJA, pre-Johnnie Formation sedimentary rocks, Johnnie Formation, Stirling Quartzite and the lower portion of the Wood Canyon Formation are Neoproterozoic in age.