The Geological History of Wasatch Back Heber

The Wasatch Back, encompassing areas like Heber Valley, is a region rich in geological history and natural beauty. The interplay of various geological processes has shaped its landscape, creating unique features that attract outdoor enthusiasts and researchers alike. This article delves into the geological history of the Wasatch Back, focusing on the formation of the Wasatch Plateau, the impact of faulting, landslides, and glaciation, and the early settlement of Heber Valley.

The Wasatch Plateau: A Table-Like Mountain Range

The Wasatch Plateau is located south and east of the southernmost part of the Wasatch Range in central Utah. It is situated in the transition zone between the Colorado Plateau and the Basin and Range physiographic provinces. The plateau is a table-like mountain range with an abundance of lakes and reservoirs along its axis.

These many lakes and reservoirs are the result of three very different geological processes that continue to shape the area. These include landslides, which are responsible for most of the plateau’s smaller lakes; extensional faulting, which created valleys (or grabens) that accommodate the plateau’s largest modern reservoirs as well as a few mid-size lakes; and Pleistocene-age (about 2.6 million to 12,000 years ago) glaciation, which created many of the plateau’s smaller high-elevation lakes. The Wasatch Plateau is home to many mid- to high-elevation wooded shallow ponds and lakes that create amazing opportunities for camping, fishing, and recreating.

Landslide morphology showing the pond-forming, closed depressions that develop below the head of a landslide.

Landslides and Sag Ponds

Most do not realize that the small, relatively flat basins that house many of these lakes are actually closed depressions that form near the uppermost part, or head of large ancient landslides. Although the bottom, or toe, of landslides can often form lakes as they dam stream drainages, few of these types of lakes last because they are prone to overtopping and erosion. However, the top part of landslides commonly form what is known as a sag pond or closed depression just below the head.

The Wasatch Plateau contains many of these with classic examples existing in areas such as Mayfield Canyon’s Twin Lake or the many ponds in the Spring Hill area and other headwaters of Twelvemile Creek. Ponds can also form between the toe and head of the landslide due to the uneven, jumbled, or hummocky topography, such as Slide Lake west of Joes Valley Reservoir.

The abundance of ancient landslides that created these lakes and ponds is largely the result of the composition of the North Horn Formation. This formation formed during the Late Cretaceous Period and Early Paleocene Epoch, approximately 75 to 60 million years ago, and consists of a series of alternating layers of sandstone and clay-rich siltstone and mudstone. These clay-rich layers make the formation particularly susceptible to landslides. When wetted, the clay layers become weak surfaces that allow the rock layers on top to move down slope.

Occasionally, the instability of the North Horn and a few other similar geologic units has led to massive modern landslides and debris flows that have caused significant damage to infrastructure on the plateau. One such example occurred in Twelvemile Canyon, which has a long history of damaging landslides. In the spring of 1983, a massive landslide in the canyon temporarily blocked the creek, which soon overtopped the natural dam and created a debris flow. The debris flow traveled 2.4 miles down the South Fork of Twelvemile Creek before burying part of Pinchot Campground. Another 1983 landslide, below nearby Twin Lake, closed the road and threatened to block Twelvemile Creek entirely. Less than two decades later, in 1998, another large landslide from the North Fork of Cooley Creek traveled 1.8 miles down the South Fork of Twelvemile Creek, depositing large amounts of landslide material in the creek. In addition to these historical landslides, prehistoric landslides are common in the canyon, and evidence shows that some have blocked and deflected creeks.

Block diagram showing the formation of a graben between normal faults as Earth’s crust extends and pulls apart.

Extensional Faulting and Graben Lakes

The second process responsible for the location of the largest lakes on the Wasatch Plateau is extensional faulting. The Wasatch Plateau has many north-to-south-oriented normal faults that are created by the incredibly slow westward extension or pulling apart of the plateau. The rocks on either side of a normal fault move up or down relative to each other and the down-dropped side creates a depression or valley called a graben. Several major Wasatch Plateau lakes, such as Scofield Reservoir and Joes Valley Reservoir, are located in such fault-bounded valleys. A string of smaller graben lakes also exists along the upper axis of the Wasatch Plateau in the Island Lake and Three Lakes area of White Mountain.

Glaciation and Cirque Lakes

The third factor responsible for the many lakes on the Wasatch Plateau is glaciation. During the Pleistocene the upper elevations of the plateau accumulated several sprawling glaciers. Existing mostly above an elevation of 9,500 feet, these glaciers carved out many notable steep-sided, bowl-shaped depressions called cirques, leaving behind several small lakes and ponds called tarns. Some examples of lake basins formed by glaciation are Ferron Reservoir, Blue Lake, and Emerald Lake, which are located in the high southeast section of the Wasatch Plateau.

Many of the Wasatch Plateau’s lakes are visible in this aerial image looking southward along the axis of Skyline Drive east of Gunnison, Utah. Deep Lake, the WPA ponds, and many of the other unnamed lakes and ponds of the Step Flats area are sag ponds created at the head of landslides within the Twelvemile Creek drainage. Island Lake and several other small lakes along the axis of the Plateau are graben lakes bounded by normal faults. Solid and dashed orange lines are normal faults, the bar and ball symbol indicates the down-dropped side of the fault. Emerald Lake is in a Pleistocene-age glacial cirque.

Heber Valley: Settlement and Development

Originally discovered by the Ute tribe, the Heber Valley served as a summer hunting ground. On July 24th, 1847, Brigham Young declared, “This is the place” and moved the pioneers into the Salt Lake Valley. But Heber Valley, caught between Salt Lake and Provo, could not be settled until there was a road through either Parley’s Canyon or Provo Canyon. Mormon church leaders sent exploratory parties to settle the territory. In 1852, J.D. However, it took another six years to establish a settlement. Settlements in Utah Valley found a direct route from the immigrant trail to Provo. A road up Provo Canyon and through what is now the Heber Valley would save immigrants, traders and the military time and money. In 1855, the Provo Canyon Road Company was established.

By late summer of 1858, ranchers from Utah Valley were grazing cattle in what they called “New London,” since most of surveyors immigrated from England. Finally in 1859, a road linked Provo with Heber Valley-allowing pioneers to settle Heber, Midway, Charleston and Daniels. Most of the initial settlers were immigrants from England who were converted to Th e Church of Latter-Day Saints by Heber C. The first homes were built in 1860 from locally quarried red sandstone, adobe and brick. Many of those homes and buildings still line historic Main Street. In 1862, the Utah Legislature made Heber the county seat of Wasatch County.

Heber’s economy depended on agriculture, livestock and dairying. By the mid-1960s, demands changed. Milk and cream from the Heber Valley Milk Depot no longer shipped in bulk and the demand for coal and oil was replaced with natural gas and electricity.

The Wasatch Fault

According to Austin Elliott, an Oxford geo-scientist who knows these sorts of things, the Wasatch Fault is the world’s best-studied normal fault. Thus, people like Elliot know quite a lot about the seam in the Earth’s crust that defines the Wasatch Front. Most of us actually living on or near the Fault, however, don’t know squat. The Wasatch Fault forms a boundary between the relatively stable North American plate and the collapsing crust of the Great Basin and Range to the west.

Slowly, so slowly we seldom notice it, the Salt Lake Valley is sliding away to the west, slipping off the Wasatch Mountains earthquake by earthquake. Of course, lots of other forces have been at work on the Wasatch, too, making the mountains we know now. Ancient glaciers formed the smooth U-shaped valleys. Much, much later, rivers cut V-shaped valleys as they found their way downhill to the Prehistoric Lake Bonneville and its remains, The Great Salt Lake, and carved the floor of the big valley between the Wasatch Front and the Oquirrhs.

But the big work was done when the Wasatch Fault’s movement cut through the moraines, slicing through them and lifting them up into the steep, jagged cliffs that give us a view of the interior history of the Earth. You can see the Jurassic Period in the reddish rocks up Parley’s Canyon. Near the mouth of the canyon, Suicide Rock is a relic of the earlier Triassic age. Lower portions of Big Cottonwood Canyon have billion-year-old Precambrian rock. The exposed portion of Timpanogos is limestone and dolomite from the Pennsylvanian period, about 300 million years old. Little Cottonwood Canyon has relatively newer rock: A molten igneous mass bubbled up near the surface a mere 32 million years ago.

And our Fault is what caused the stair stepping Benches, defining the value of Valley’s real estate. We’ve known about the Wasatch Fault in theory since the 1890s, but that hasn’t stopped us from building steadily on it and around with little heed to the whole earthquake thing.