Geologic Points of Interest by Activity - Mountain Ranges/Basins

Laccoliths are certainly among the most unique and interesting geologic features, and Utah has some of the premier examples in the world. Best known are the Henry and La Sal Mountains laccoliths because of their spectacular exposures, but the Pine Valley Mountains and several nearby intrusions are also excellent laccoliths. The Pine Valley Mountains laccolith may be one of the largest in the world. A laccolith is formed when an intrusive body from below uplifts a region (see diagram below). It is like a volcano that did not quite make it to the surface. The Pine Valley laccolith was emplaced about 21 million years ago as molten rock from deep within the earth moved upward into shallow overlying sedimentary rocks. There it spread out and crystallized into what is one of the largest such intrusions in the world; uplift and erosion have since uncovered this granite-like rock. (From: Survey Notes, Utah Geological Survey, Sept. 2002, v. 34).

Head south on I-15 from Salt Lake City, UT. Take the Scipio exit (188) to US Highway 50. Travel 30 miles on Highway 50 to Salina. Travel from Salina to Sigurd on I-70 (take exit 48, which is the start of Utah Highway 24). Follow Highway 24 south to the Fish Lake turnoff (Utah Highway 25, the Fish Lake Scenic Byway).

Travel north on I-15 from Southern Utah or Cedar City, UT. Take exit 95, travel southeast on Utah Highway 20 for 21 miles. Then take US 89 north to Kingston. At Kingston, take US Highway 62 east and then north at Otter Creek Reservoir to its junction with Utah Highway 24. Head south on Highway 24 to the Fish Lake turnoff (Utah Highway 25, the Fish Lake Scenic Byway). Follow Utah Highway 25 northeast 13 miles to the end of the byway. Here you will enter the Fishlake National Forest about three miles along the route.

Much of the underlying rock of Fish Lake Basin is composed of basalts that flowed from fissures then cooled. The basin itself formed when one block dropped down between two faults on either side. On the southeast side of the lake lie the slopes of Mytoge Mountain and on the northwest side, Fish Lake Hightop Mountain.

The fault blocking occurred at different times and at different places along a10 mile stretch. The ends of the basin have not settled concurrently as recent evidence suggests that the lake once drained to the south rather than its current route to the north at Lake Creek.

Glacial activity also played a role in carving canyons and depositing moraines in Fish Lake Basin. Well-noted evidence of this activity is at Pelican Canyon (Godfrey.)

This is located in the eastern most portion of the Fishlake National Forest. Head south on I-15 from Salt Lake City, UT. Take the Scipio exit (188) to US Highway 50. Travel 30 miles on Highway 50 to Salina. Travel from Salina to Sigurd on I-70 (take exit 48, which is the start of Utah Highway 24). Follow Highway 24 south towards the town of Loa (At milepost 41, Thousand Lake Mountain is directly ahead). Before reaching Loa turn and head northeast towards Fremont. From Fremont, go 5 miles north on UT-72 and go southeast on Baker Ranch Road, which then curves northeast and joins the Cathedral Valley Scenic Byway. The road turns south again and loops back to UT-72.

A portion of the Great Western Trail crosses Thousand Lake Mountain north and south. Campsites and hiking opportunities abound. On the eastern side of the mountain lies, the very colorful and much less visited portion of Capitol Reef National Monument named Cathedral Valley. Stunning mountainous terrain drops to red valley floors dotted with amazing monoliths and other red rock features.

Thousand Lake Mountain, made up of Miocene volcanic rocks, capped by Pliocene lava flows (Chronic, 1990.), is a misnomer when one considers how few lakes really exist in its boundaries in comparison to the nearby Boulder Mountain.

Volcanic rocks that flowed rather fluidly from vents and fissures to form relatively flat surfaces cap Thousand Lake Mountain. Beneath the volcanics lie the Mesozoic sedimentary formations of the Moenkopi, found on the south side, and the Mancos Shale to the north. However, landslide debris buries most of these colorful formations and gives Thousand Lake Mountain its distinctive shape. This is due, in part, to high relief as well as the sequence of rocks present.

In the much cooler, wetter periods of Utah's history, such as 10,000 years ago, landslides were much more prevalent than today. Water seeping into the fractured volcanic cap rocks was forced to move laterally once it met the impermeable shale. The water would also turn shale into slippery clays creating less friction for the cap layers. This combination effectively caused the cap layers to slide (Godfrey.) 

From I-70, exit at the town of Elsinore just south of Richfield, UT. Head east towards the town of Nibley and then turn south on State Highway 118 towards Monroe. Continue on State Highway 118 as it veers southeast and turns into Forest Road 078.

Flood deposits seen along the walls of Pole Canyon attest to the dramatic volcanic history behind the formation of Monroe Mountain. About 25 million years ago, two volcanic centers, near Signal Peak and Langdon Mountain, violently erupted clouds of volcanic ash, dust, and smoke to produce localized thunderstorms. Torrential floods cascaded down the newly formed volcanic flanks carrying boulders and debris. Since large amounts of material had been removed from the magma chamber creating a large void, the overlying material collapsed and formed the Monroe Peak Caldera measuring about 14 by 11 miles.

A quiet period of erosion and meandering streams ensued from 14 to 7 million years ago. The Sevier River Formation is the result of sediments deposited in channels, swamps, and lakes.

Earthquake activity beginning about five million years ago led to the lifting and bending of large blocks of crust, including Monroe Mountain. Valley floors dropped while mountain slopes lifted. The repeated shaking and slope instability generated many landslides (Thompson Creek Landslide near Monroe, Elbow Landslide near Marysvale, and the Brink near Burrville).

The Pahvant Range lies just west of Richfield, UT, extending south where I-70 works its way through the divide between the Tushar Mountains and the Pahvant Range, to the north where Scipio lies. The Canyon Mountains to the north of the Pahvant Range are separated by a divide that I-15 traverses.

The east side of the Pahvant Range differs widely from the west in age, composition, formation, and deformation. The west side of the Pahvant Range consists of drab colored, Paleozoic marine deposits including limestones, quartzites, sandstones, and shales. Compressional forces due to continental collision thrust those layers up and over other sedimentary layers creating a high mountain range. On the east, those ancient mountains shed their deposits, forming colorful red and yellow Tertiary age conglomerates, sandstones, and shales at their base.

The west side is well weathered and eroded with steep slopes and tall cliffs as well as the fact that the rocks dip nearly vertical. The east side is rounded and nearly flat lying. Faults are still active in the area causing the range to continue to uplift.

The bulk of the Canyon Mountains are similar to the west side of the Pahvant Range (Godfrey.)

From Highway 89, south of Richfield, UT, just past Big Rock Candy Mountain, to the west begins the Tushar mountains. They continue south and end near Circleville, UT. Highway 89 offers the eastern view of this range.

The Tushar Mountains consist of the Bullion Canyon Volcanics from 22-35 million years ago and the Mount Belknap Volcanics from roughly 21 million years ago. Catastrophic eruptions with large volumes of ash deposited as far north as Richfield formed the Joe Lott Tuff Member and led to the collapse of the Mount Belknap caldera 19 million years ago. 

Fluvial, eolian, and glacial activity has largely eroded these volcanics. Driving through Marysvale Canyon (see Big Rock Candy Mountain below) reveals a profile of the volcano's flank and several flows to the east. Sulphur laden deposits with their distinctive yellow color are also visible in this region and attest to the later stages of the volcanic activity (Godfrey.)

Adjacent to Mt. Moriah is The Table, a Forest Service Research Natural Area consisting of a broad, 7000-acre, mildly sloping plateau at 11,000 feet, having a unique environment of alpine plants and wind-battered bristlecone pines. The open topography of The Table affords excellent views of Mt. Moriah and the surrounding terrain. The Mt. Moriah Table contains subalpine bristlecone forest, grasslands, and a minor shrubland community in good to excellent condition and supports an extensive mosaic of subalpine steppe grassland dominated by blackroot sedge and purple reed grass with minor inclusions of the Goldenbush purple reed grass shrub steppe. Remnant grasslands such as found within the RNA are uncommon on the Humboldt-Toiyabe National Forest. Open bristlecone pine forests and Engelmann spruce occupy gentle to steep terrain at the lower elevations in the RNA. Individual bristlecone trees in the open woodlands are 20 to 25 feet in height. An optional side trip to the Big Canyon cirque on the northeast flank of Mt. Moriah offers additional rugged mountain scenery.

The broad, arch-like physiography of the northern Snake Range is shaped by its geology, which is unique in the region. It is a classic example of a Cenozoic metamorphic core complex. The most prominent structural feature is the Northern Snake Range Decollement (NSRD), a low angle fault that juxtaposes an upper plate of Paleozoic and Tertiary strata against a lower plate of metasedimentary and igneous rocks. The NSRD is spectacularly exposed along the deeply incised canyon walls and beneath Mt Moriah on The Table. (From: Lee et al. 1999)

The Sawtooth Ridge is along the boundary between Yosemite National Park and the Hoover Wilderness. This beautiful high Sierra backcountry can be easily accessed. The ridge is a beautiful display of glacial alpine sculpture including arêtes, cols, horns, hanging valleys, rock basins, and cirques. 

This area has long been known for its good rock climbing, breathtaking knife-edge ridges, and spectacular spires. This area is known for several classic alpine rock climbing routes. The tallest peak in the area is Matterhorn Peak (12,264 ft.). There are several excellent routes the can be climbed in order to reach the top of this peak. The Sawtooth Ridge also hosts some of the Sierra's most spectacular skiing. You can ski through the heart of the Sawtooths in one long spring day. Nearly everyone coming to ski the Sawtooths ascends towards Matterhorn Peak via the Horse Creek trail. Popular routes to the peak include the East Couloir just left of the summit massif, the hourglass-shaped slope left of that known as Skiers Dream, and the easier but less direct Horse Creek Pass route.

This overlook offers panoramic views of the Sawtooth Mountains. It is due for reconstruction in the fall of 2007, but visitors can still see breathtaking views.

The Sawtooth Mountains are mostly composed of batholiths. The pink 44 million year old Sawtooth Batholith and the gray 70 to 90 million year old Idaho and Atlanta Batholiths.

Intense glaciation as recent at 14,000 years ago carved the rough Sawtooth Range and left glacial moraines now forested along the base of these mountains. There are also many lakes nestled within these moraines. The sawtooth appearance of the mountains is due to the pervasive vertical fracturing of the granite.