Utah has many fantastic geologic sites and views, many in national parks and monuments. Get out and explore some of the lesser known areas in the state.
Description and logging requirements:
- Do you see crystals on the rocks? If so, what percentage of the rock contains them (rough estimate)?
- How many different colors do you see in the rocks? What do you think is the cause?
- Take a photo of yourself at the coordinates with White Rock in the background. If you don't want a photo of yourself, write your caching name and the date of your find on a piece of paper - take a picture holding that in the end of the rock. Post with your log.
White Rocks is a collection of three light gray, dome-shaped hills of igneous rock in the southern Cedar Mountains in northwestern Utah.
The names White Rocks and White Rock Complex are used to refer to the three largest isolated outcrops that rise starkly above the floor of a sandy, gently sloping 2-square-mile amphitheater. The amphitheater is bounded by various types of faults and encircled by the southern Cedar Mountains. The main outcrop, known officially as White Rock, is considerably larger than the other two outcrops combined, which are informally known as “south rock” and “west rock” and are nearly the same size. A bubbling spring and pool, White Rock Spring, is at the west-edge of White Rock.
White Rocks is composed of intrusive igneous rock, meaning the rock crystalized from molten magma as it slowly cooled beneath the surface of the Earth. This area is an ancient east-west-trending zone across northern Utah and eastern Nevada, where two blocks of continental crust likely converged around 1.7 billion years ago. Much later this zone of weakness was exploited by igneous activity that swept through Utah between 40 and 23 million years ago. This igneous episode is responsible for White Rocks, dated at nearly 39 million years ago, as well as other volcanic rocks in the southern Cedar Mountains.
The White Rocks outcrops are peppered with large- to small-sized alcoves and cavities, honeycomb-type, and other weathering features on recesses, vertical walls, and below overhangs. Larger-scale rock weathering forms occur all over the main White Rock and on the north-facing sides of the south rock. Light gray in color, the rock is patterned with blotches and expanses of primarily orange and lesser yellow, black, and tea-green lichen, preferential to north-facing slopes and absent from caverns. Streaks of iron and manganese stain the rock where storm water is channeled off the domes. Vegetation is sparse; junipers, grass, and cacti grow out of scattered pockets of soil and fractures in the rock.
A miniature arch near the base on the west side.
The rock of White Rocks is an attractive porphyritic dacite. Common to volcanic domes such as the Mt. St. Helens lava dome in Washington State, dacite is intermediate in composition between andesite and rhyolite. Porphyritic rock has large, visible crystals called phenocrysts in a finer-grained groundmass. The easily observable phenocrysts of White Rocks constitute about one-quarter of the rock. White plagioclase feldspar forms the largest crystals, accompanied by fractured, gemmy quartz, and flecked with blackish-brown biotite and amphibole. The grayish groundmass is an intergrowth of plagioclase, potassium feldspar, and quartz.
Virtual view of White Rocks using the Rush Valley 30’ x 60’ quadrangle geologic map from the UGS. Oblique view to the west with satellite base map. The pink hills are the three main outcrops at White Rocks and are surrounded by a plain of sand and silt—yellow and white with red dots. Limestone (blue) and lava flows (brown) encircle the White Rocks amphitheater. White Rock, at right, is about 44 acres and rises some 375 feet from the amphitheater floor. The nearby second white rock (south rock) rises 185 feet in height and is 12 acres in size, and in the distance, at left, the third white rock (west rock) rises 145 feet in height and covers 10 acres.
(White Rocks, Tooele County, Utah, published August 2020 by Jim Davis, via geology.utah.gov)
There are no services in Skull Valley. Go with sufficient fuel and supplies. White Rock has tall cliffs, steep slopes, and loose and crumbling rock surfaces; use caution when traversing the rock. The White Rocks area is frequented by climbers, scouts, horse riders and target shooters. Autumn and spring are the most pleasant times of year to visit. Approximately a dozen primitive, dispersed, first-come-first-served campsites are around the bases of the White Rocks, most at the main rock. There are no developed facilities, water, or restrooms. No fees are required. Dogs are allowed.