Signs on display at the Park City Sunrise Rotary Regional Geologic Park.

GeoSights: Park City Sunrise Rotary Regional Geologic Park, Summit County, Utah

SURVEY NOTES

GeoSights: Park City Sunrise Rotary Regional Geologic Park, Summit County, Utah

by Mark Milligan and Robert F. Biek


Signs on display at the Park City Sunrise Rotary Regional Geologic Park.

Signs on display at the Park City Sunrise Rotary Regional Geologic Park.

After 4.5 billion years of geologic evolution, 35 million years of turning wood into stone, two decades of community vision, and a year of developing informational signage, the Park City Sunrise Rotary Regional Geologic Park was unveiled at a ribbon-cutting ceremony on September 21, 2019!

In 1997 a heavy equipment operator uncovered an enormous 5- to 10-ton piece of petrified wood while excavating a water line near Silver Creek Junction, roughly 5 miles north of Park City’s historic downtown. This discovery from an area already known for smaller pieces of petrifi ed wood prompted members of the Park City Sunrise Rotary Club to begin searching for a way to create a space devoted to telling the amazing story of the area’s unique geology. They approached developer Matt Lowe as he began planning a new subdivision, Silver Creek Village. Mr. Lowe liked their idea and subsequently dedicated the space and constructed the Regional Geologic Park to tell the story of the petrified wood and its interconnections with the Park City mining district, local ski resorts, beautiful mountain scenery, and other aspects of the natural history of the Park City area.

The park includes a welcome panel, nine information panels, and specimens of petrified wood. The signage includes something for everyone, from the casual visitor to geology students on fi eld trips and traveling geologists. Here are some highlights from the panels.

Geologic Foundation: The modern landscape surrounding the Regional Geologic Park is built upon geologically ancient events. Two continental-scale features dominate the geology of the greater Park City area: the north-south trending Utah hingeline and the east-west-trending Uinta-Cottonwood arch. Both owe their origin to the formation and subsequent break-apart of the supercontinent Rodinia, between 1.7 billion and 780 million years ago.

Keetley Volcanics: Roughly 30 to 40 million years ago, active volcanoes towered over the area. The volcanic rocks (known as the Keetley Volcanics) and related igneous intrusions are responsible for the petrified wood and mineralization in the Park City mining district. For more information see Survey Notes, v. 50, no. 3, p. 4–5.

Ancient Landscape: What did the region look like 35 million years ago? Volcanoes pocked the landscape and explosive eruptions of rock and ash leveled forests that provided the area’s petrifi ed wood.

This 5-by-8-foot petrified log collected near the park was sliced into massive slabs, three of which are on display throughout Summit County. This slab is at the Courthouse in Coalville, one is at the Sheldon Richins Building at Kimball Junction, and one is at the Justice Court near the Regional Geologic Park. Photo by Tom Gadek.

This 5-by-8-foot petrified log collected near the park was sliced into massive slabs, three of which are on display throughout Summit County. This slab is at the Courthouse in Coalville, one is at the Sheldon Richins Building at Kimball Junction, and one is at the Justice Court near the Regional Geologic Park. Photo by Tom Gadek.

Petrified Wood: Following burial from eruptions, glass shards in volcanic ash weathered to form mineral-rich groundwater, providing silica that slowly turned wood to stone.

Park City Mining: Park City was born as a mining town. At its peak, the Park City mining district had 300 operating mines and 1,000 miles of tunnels. From 1875 to 1982 the mines produced 1.45 million ounces of gold, 253 million ounces of silver, 2.7 billion pounds of lead, 1.5 billion pounds of zinc, and 129 million pounds of copper! The rich ores owed their existence to mineral-rich hydrothermal (hot) fluids circulating from the magma which fed the Keetley volcanoes.

Modern Landscape: Tectonic-scale forces and erosion created Utah’s current landscape in the 35 million years since forested volcanoes loomed over the area. Today, Utah contains parts of three physiographic provinces, each with distinctive landforms and geology: the Basin and Range Province, the Colorado Plateau, and the Middle Rocky Mountains, where the Regional Geologic Park is located.

Ice Age: During the most recent Ice Age in Utah, glaciers blanketed high mountain valleys and peaks, and Lake Bonneville covered most of Utah’s western valleys. The fi rst extensive collection of Ice Age land animals from Utah was discovered in 1963 about a half mile northwest of the Regional Geologic Park.

Water: Park City lies within the Snyderville drainage basin, an area of complex geology that is interesting to geologists but frustrating to water managers, real estate developers, and politicians. To meet growing demands for water in the Park City area, suppliers have utilized creeks, springs, mine drainage tunnels, groundwater, and imported water from outside the basin. Geologic Maps: Perhaps the best way to communicate the complex geologic story of the Park City area is through geologic maps. A geologic map is a tool that can be used in many ways—from learning about the geologic history of an area, to natural resource and hazard assessment, to providing information for intelligent land-use planning and growth. For more information see Utah Geological Survey Public Information Series 66.





How to Get to The Regional Geologic Park:

From the Wasatch Front, head east on Interstate 80 to exit 146 for U.S. Highway 40/189 toward Heber City/Vernal. After the interchange take the first exit (exit 2) for Silver Summit. At the end of the off-ramp turn left (east) onto Silver Summit Parkway, which becomes Silver Creek Drive after crossing over the highway. In less than a quarter mile from U.S. Highway 40/189, at the traffi c circle, take the third exit onto Pace Frontage Road (northbound). After half a mile turn right (east) onto Old Forest Road. The park is located a couple hundred yards past the intersection on the left.

From Park City’s historic downtown, head east on Kearns Boulevard (UT 248) to U.S. Highway 40/189 and go north. Take exit 2 for Silver Summit. At the end of the off-ramp turn right (east) onto Silver Creek Drive and follow the directions above.

GPS Coordinates: 40°43’37” N 111°29’23” W


GeoSights: Pine Park and the Ancient Supervolcanoes of Southwestern Utah

SURVEY NOTES

GeoSights: Pine Park and the Ancient Supervolcanoes of Southwestern Utah

By Lance Weaver


Hidden in a remote corner of Washington County is a fascinating place nearly forgotten among the other attractions of southern Utah. The scenic Pine Park area exposes intriguing volcanic deposits that reveal the story of the largest volcanic eruptions in Utah’s geologic history. Although the beautiful exposures outcrop in only a small area, the eruptions that produced the volcanic deposits in this part of Utah were some of the largest in Earth’s history.

Exposures of the Tuff of Honeycomb Rock at Pine Park.

Exposures of the Tuff of Honeycomb Rock at Pine Park.

Pine Park is located approximately 20 miles (32km) southwest of Enterprise in the southwest corner of Utah. It is one of several attractions located on the upper Beaver Dam Wash. The region supports a high desert forest of juniper, pinyon, and large ponderosa pine trees, which thrive in the well-drained volcanic soils. The main attractions in Pine Park are bright white volcanic ash-flow tuff exposures that form a landscape of hoodoos, pyramid- and mushroom-shaped domes, and undulating slickrock basins. Many of these vistas resemble the hoodoos and knobs of the better-known Goblin Valley State Park of central Utah, or the Toadstools area near Lake Powell’s Wahweap Bay. However, instead of the familiar sandstone and claystone of Utah’s Colorado Plateau, these spires have eroded from thick deposits of white volcanic ash-flow tuff known as the Tuff of Honeycomb Rock. An ash-flow tuff is a type of rock made of volcanic ash, rock, and gases derived from explosive volcanic eruptions.

A few miles to the west down Pine Park Canyon, at Beaver Dam State Park in Nevada, the same types of ashflow tuff deposits create scenic vistas like those of Pine Park. These two attractions showcase just a small piece of the voluminous ash-flow tuff deposits that blanket the region. Called “supervolcanoes” or “super-eruptions” because of their immense size, these types of eruptions tend to leave behind massive, often miles-wide, craters called calderas instead of the typical pyramid-shaped cones of stratovolcanoes. A caldera’s large, cauldron-like hollow or valley forms after magma erupts and the ground surface above the magma chamber collapses.

Miocene- to Oligocene-age (12 to 36 million years ago) supervolcanoes, caldera complexes, and volcanic deposits, which stretch from south-central and western Utah through Nevada and eastern California. From Best and others, 2013, Geosphere article: https://doi.org/10.1130/GES00945.1

Miocene- to Oligocene-age (12 to 36 million years ago) supervolcanoes, caldera complexes, and volcanic deposits, which stretch from south-central and western Utah through Nevada and eastern California. From Best and others, 2013, Geosphere article: https://doi.org/10.1130/GES00945.1

Pine Park lies at the edge of the ancient Pine Park caldera—one of dozens of calderas spanning from southwestern Utah, across central Nevada, to the border of eastern California. These supervolcanoes were active between 12 and 36 million years ago, when Utah was home to rhinoceros, camels, tortoises, and palm trees. Although the Tuff of Honeycomb Rock that outcrops at Pine Park is locally derived from a smaller ancient caldera, many of the ash-flow tuffs in the area are derived from the nearby Indian Peak–Caliente caldera complex, formed by some of the largest ancient super-eruptions in North America. Geologists have found deposits 2.5 miles (4 km) thick that are believed to have come from a single incredible eruption from the Indian Peak–Caliente caldera complex 30 million years ago. Over 1,300 cubic miles (5,400 km3) of volcanic materials have been found from this eruption spanning from central Utah to central Nevada and from Fillmore, Utah, on the north to Cedar City, Utah, on the south—over 1,000 times the volume of material ejected during the 1980 Mount St. Helens eruption (about 1 cubic mile [4 km3]). And this caldera was only one of up to 20 calderas in the region.

Since the eruption of the volcanoes that created the deposits of Pine Park, extension of the Earth’s crust across the Basin and Range Province has torn apart much of western Utah and has vastly altered the landscape and drainages. Without geologists studying the thick volcanic deposits such as those exposed at Pine Park, people may have never known the extent to which ancient volcanoes altered the landscape of this part of southern Utah.

How to Get There:

To get to Pine Park, head west on Main Street from the town of Enterprise, Utah, toward Panaca on State Route 219. Continue past the signs pointing to Enterprise Reservoir. After a few miles the paved road will transition to a nicely graded dirt road. After driving 12.6 miles from Enterprise, take a left on Forest Service Road 001 (White Rocks Road) and continue west-southwest 9.5 miles. Along the last mile, the road becomes rougher and turns sharply to the southeast and snakes its way down into the valley. The road ends at a creek and primitive campsite. There are no bathroom or potable water facilities.

GPS Coordinates: 37° 31′ 19.4″ N 114° 01′ 22.5″ W

GeoSights: Hole-in-the-Ground, Snake Valley, Millard County, Utah

GeoSights: Hole-in-the-Ground, Snake Valley, Millard County, Utah

by Mark Milligan

Hole-in-the-Ground is just that, a sinkhole created by the roof collapse of a buried limestone cavern. It is massive. A hole that measures over 250 feet wide and up to 110 feet deep on an otherwise flat valley floor is an impressive sight to see.

North-south-trending mountain ranges separated by broad and flat valleys characterize the Basin and Range physiographic province, which extends from the Wasatch Range across western Utah and westward to the Sierra Nevada in California. The valleys typically contain thousands of feet of sediment shed from their bounding ranges. However, this sediment does not always have a consistent thickness across a valley. Some locations have seemingly isolated rock outcrops of low-lying hills away from a range front. Nonetheless, when standing on a valley floor you tend to assume solid rock lies a great distance below your feet. Hole-in-the-Ground creates a portal into the subsurface that shows these assumptions and generalizations can be wrong. The walls of this sinkhole expose approximately 320-million-year-old (Mississippian- to Pennsylvanian-age) bedrock of the Ely Limestone a mere 30 to 40 feet below the surface. A buried fault is thought to have elevated the shallow bedrock.

Sinkholes form by dissolution of underlying limestone bedrock, a process in which acidic groundwater dissolves part of the limestone and carries it away in solution. This creates a cavity which can continue to grow until the roof is unable to support its own weight and that of the overlying sediment. The collapse may occur as a single catastrophic event or a progressive series of smaller failures.

Whereas sinkholes in places like Florida and Kentucky pose a threat and sometimes swallow houses or the National Corvette Museum (a sad story, look it up), Hole-in-the-Ground is over 5 miles from Eskdale, the nearest settlement, and thus poses no risk to any structures. Even cattle are protected by an enclosing wire fence. Furthermore, the timing of this sinkhole is unknown. Collapse may have started as long ago as a million years.

Hole-in-the-Ground lies within Snake Valley, which was flooded by ancient Lake Bonneville approximately 18,000 years ago during the most recent Ice Age. The rim of the sinkhole lies roughly 550 feet east of and 20 feet above the ancient lake’s highest shoreline, named the Bonneville Shoreline. Thus, the bottom of the hole, being over 75 feet below ancient lake level, would have likely been a swimming hole filled with shallow groundwater related to the lake. Additionally, Lake Bonneville deposited impressive V-shaped sand spits, the closest of which lies less than half a mile to the southwest of the sinkhole.


How to Get There

The sinkhole is located on land administered by the U.S. Bureau of Land Management about 6 miles northeast of the small unincorporated community of Eskdale in western Millard County. This area is remote, so please plan accordingly. Eskdale has no services; the closest gas is available in Baker, Nevada, about 15 miles to the southwest.

From the Wasatch Front, head south on I-15 towards Nephi. Take exit 225 and turn right onto Utah State Route 132 (100 North). After 34 miles, turn left onto U.S. Route 6. After 16 miles, turn right onto U.S. Route 6/50. After 84.6 miles, turn right onto the paved two-way road towards Eskdale. There are no road signs beyond this point. Continue by using GPS navigation or the indicated mileage, beginning where you leave U.S. Route 6/50:

3.7 miles Turn RIGHT at the T-intersection.

0.4 miles Turn LEFT.

0.9 miles Turn RIGHT. (Pavement ends in Eskdale.)

0.6 miles Road curves to the left.

0.2 miles Continue straight/north at junction.

4.5 miles Turn RIGHT onto the unimproved two-track dirt road, which is passible in moderate to high-clearance vehicles. Proceed with caution or walk in.

0.7 miles End at sinkhole. The hole is surrounded by a wire fence, presumably to keep cattle out. The southwest corner of the fence has a stile for access.

Coordinates: 39.175017°, -113.902319°.

The sinkhole is located on the Hole-in-the-Ground 7.5-minute quadrangle map.


Survey Notes, v. 51 no. 1, January 2019