The Great Yosemite Road Trip

Mile 0 to 60Front Range out of Denver. Precambrian granite-gneiss ~1.7 billion years old, the same ancient core that builds Pikes Peak. The Continental Divide crosses at the Eisenhower Tunnel (mile 213).

Mile 116Glenwood Canyon. I-70 squeezes through 1,300-ft vertical walls of Mississippian limestone (~340 million years old), carved by the Colorado River. Considered an engineering marvel, the highway is cantilevered above the river.

Mile 70Grand Mesa appears to the south, the world’s largest flat-topped mountain, capped by 10-million-year-old basalt flows over softer Cretaceous sediments.

Mile 25 to 0Book Cliffs rise on the north (tan-gray Cretaceous shale and sandstone, ~80 million years old). To the south, Colorado National Monument’s burnt-orange Wingate Sandstone cliffs (Triassic, ~210 my). Rabbit Valley sits at the transition from the Rockies into the Colorado Plateau.

I-70 mile 230 to 160Book Cliffs continue along the north side, same Cretaceous coals and shales. To the south, the land starts to corrugate as you enter the San Rafael Swell.

I-70 mile 130 to 95San Rafael Swell. A giant earth fold (anticline) pushed up ~60 million years ago in the Laramide Orogeny, the same mountain-building episode that built the Rockies. I-70 cuts straight through the upturned layers, exposing Permian rock (290 my) at the core out to Cretaceous (~80 my) at the edges. The jagged vertical strata are the “Reefs.”

UT-24 southGoblin Valley’s hoodoos are Entrada Sandstone (Jurassic, ~170 my) eroded into mushroom shapes by water sorting harder layers from soft.

US-50 mile 65 to 35After Salina, US-50 enters the Sevier Valley a structural valley between the Pavant Range (west) and the Wasatch Plateau (east). This is the geologic boundary where the Colorado Plateau ends and the Great Basin begins.

Across NevadaYou’re now in the Basin and Range Province a 200,000-square-mile region of internal drainage where no water reaches the ocean. Every ridge you see is a fault-block mountain: a slab of crust tilted up between extensional faults that are slowly pulling Nevada apart.

Approaching BakerThe snow-capped peak ahead is Wheeler Peak (13,065 ft) tallest in Nevada outside the Sierra. The Snake Range holding it up is granite + quartzite with bowl-shaped glacial cirques from the last ice age. The bristlecone pines on its flanks are some of the oldest living things on Earth (5,000+ years).

Lehman Caves is a karst cave dissolved into Cambrian Pole Canyon Limestone (~500 million years old). The cave is famous for its rare “shields”, flat parallel discs that grow out of cracks in the wall, found in only a few caves worldwide.

Wheeler Peak Scenic DriveClimbing the Snake Range granite, quartzite, and limestone uplifted along normal faults during ongoing Basin-and-Range extension (Nevada is actively stretching at ~1 cm/year).

Alpine Lakes LoopStella and Teresa Lakes sit in glacial tarns bowls scoured by ice and dammed by moraine debris. The cirques here held small glaciers as recently as the Little Ice Age (~1850). Look for glacial striations parallel scratches in the polished bedrock left by rocks dragged under the ice.

First 30 miClassic Basin and Range each pass crosses a fault-block range, drops into the next valley. The pattern repeats for 380 miles of US-50 across Nevada.

Ely, NVOld copper-mining town on the Robinson Mining District a porphyry copper deposit ~110 million years old (the same Mesozoic intrusive episode that built the Sierra Nevada batholith visible at D.L. Bliss).

Eureka, NV (mile 75)Lead-silver mining town on ~40-million-year-old Eocene volcanic rocks. The wide valleys between ranges are filled with thousands of feet of sediment shed off the ranges over the last 15 million years.

Austin, NV (mile 165)Sits on the Toiyabe Range. The pass east of town (Austin Summit, 7,484 ft) crosses Paleozoic limestone and silver-rich Tertiary volcanics.

Sand Mountain (mile 295)A 600-ft tall singing dune east of Fallon, windblown sand from the ancient Lake Lahontan bed, the Ice Age lake that once filled half of western Nevada. The dune “booms” when sand avalanches down its lee face.

Fallon → Carson CityDriving across the Carson Sink lowest point of the old Lake Lahontan basin. To the south the Stillwater Range rises sharply.

Carson City → TahoeThe Sierra Nevada appears ahead, the world’s largest fault-block range uplifted nearly two vertical miles on its east face. Granite of the Cretaceous Sierra Nevada batholith (~100 my), same rock as Half Dome. The Tahoe basin itself is a graben a block that dropped down between the Sierra crest and the Carson Range during Basin-and-Range extension. Glaciers carved and polished the shoreline at Lester Beach.

CA-89 S to US-395Dropping off the Sierra’s west flank and into the Walker River canyon. The east face of the Sierra Nevada is one of the most abrupt fault scarps on Earth, 10,000+ ft of relief in just a few miles, the range tilted like a trapdoor.

Bridgeport ValleyA broad graben a valley floor that dropped between parallel faults during Basin-and-Range extension. Buckeye Hot Springs are geothermally heated groundwater rising along one of those faults, the same tectonic activity that built the volcanic landscape south of here.

US-395 S to Lee ViningPassing the Mono Craters on the right, a chain of young rhyolite domes, the youngest erupted only 650 years ago. Mono Lake comes into view: 760,000 years old, hypersaline, rimmed with tufa towers that formed underwater when calcium-rich springs met the carbonate lake.

Tioga Pass (9,945 ft)The Sierra Crest. Bare granite domes of the Sierra Nevada batholith same 80 to 100 million year old plutons that build El Capitan. Tenaya Lake sits in a glacially scoured bowl just west of the pass.

Tioga Road eastClimbing through the Sierra Nevada batholith. Bare granite domes (Polly Dome, Pywiack Dome) are 80 to 90 million year old plutons exposed by erosion. Tenaya Lake sits in a glacially scoured bowl.

Tioga Pass (9,945 ft)Highest highway pass in California. The Sierra Crest divides the granite batholith (west) from metasedimentary rocks on the east edge.

Mono Lake760,000 years old, hypersaline (3× saltier than ocean), rimmed with tufa towers. The Mono Craters just south are young rhyolite domes, the youngest erupted only 650 years ago.

June Lake → MammothDriving along the rim of the Long Valley Caldera a 20-mile-wide supervolcano that erupted 760,000 years ago. The pinkish valley floor is Bishop Tuff from that eruption.

Owens Valley to BishopDeepest fault-bounded valley in North America 10,000+ ft of relief between the floor (4,000 ft) and White Mountains crest (14,252 ft) just east. Actively rifting along the Owens Valley Fault, same fault that caused the 1872 magnitude-7.9 Lone Pine earthquake.

US-6 / US-95 · Nevada Basin and RangeEast of Bishop the route enters the heart of the Basin and Range dozens of parallel fault-block mountains and dropped valleys formed as the crust stretched and pulled apart over the last ~20 million years. The dark, flat-topped mesas around Tonopah and Goldfield are Tertiary volcanic tuffs and lava flows from massive eruptions ~15 to 20 million years ago, the same volcanism that seeded the gold and silver which built Rhyolite and the other boom towns.

Amargosa Desert · Ash MeadowsThe turquoise pools at Ash Meadows are fed by a vast regional aquifer of “fossil water” rain and snowmelt that fell thousands of years ago, traveling underground through carbonate rock before surfacing along fault lines. Devils Hole is a window straight down into that water table. Pahrump and Amargosa sit in down-dropped basins between the Spring Mountains and the Funeral/Grapevine ranges that wall off Death Valley just to the west.

Las Vegas Valley → MesquiteI-15 crosses the eastern Basin and Range out of the Las Vegas Valley, a down-dropped basin between the Spring Mountains and the Muddy/Virgin ranges, before threading the Virgin River into Arizona’s northwest corner.

Virgin River Gorge (I-15)One of the most dramatic highway corridors in the Southwest, sheer Paleozoic limestone and sandstone walls, 1,000+ ft of relief, folded and tilted by the same compression that raised the surrounding ranges. One of the most expensive highway segments ever built ($10 million/mile in 1973).

St George · Sand HollowYou’ve climbed onto the edge of the Colorado Plateau. The orange domes around Sand Hollow and the red dunes of Sand Mountain are Navajo Sandstone Jurassic (~180 million years old) petrified sand dunes, the same formation that becomes the great walls of Zion just upriver.

Zion CanyonThe cliffs are that same Navajo Sandstone here stacked 2,000+ ft thick. The Virgin River has sawed straight down into the plateau and is still deepening the canyon today, the Narrows is the river working at the bottom of its own cut. Upstream, the Zion-Mt. Carmel tunnel (1930) bores through the sandstone past cross-bedded Checkerboard Mesa.

US-89 N · climbing the Grand StaircaseFrom Zion (~4,000 ft) the highway climbs steadily toward Bryce (~8,000 ft), stepping up through progressively younger rock layers, the Grand Staircase. Panguitch sits in a high valley along the Sevier Fault at the foot of the pink cliffs, with tomorrow’s Claron limestone hoodoos waiting just above.