Utah Geological Survey

Abstract Despite the prevalence of rock glaciers in mountain environments, their ice volumes are poorly constrained. Rock glaciers persist in settings unable to support glaciers. They act as climate resilient water stores and refugia for cold‐adapted species while also posing a hazard to alpine communities. Imaging the entire internal structure of rock glaciers and estimating their ice volumes is crucial for understanding how these impacts evolve in a warming climate. Ice volume is challenging to measure with methods typically used on glaciers, such as aerial gravity and ground penetrating radar, due to the relatively small size of rock glaciers as well as the presence of internal and overlying debris. In this paper, we use an alternative approach: the terrestrial gravity method. We model the internal structure of Timpanogos Rock Glacier, Utah, USA using a 3‐D Bayesian inversion from 232 gravity measurements. Our inversions indicate an ice volume of 1.55 × 10 6 m 3 with an average thickness of 18.8 m and an ice fraction of 83% within the ice core. Measured surface velocities are consistent with ice thicknesses produced by our gravity inversions. Using our model results and measurements from geophysical studies of 10 other rock glaciers, we synthesize a new, linear area‐volume scaling relationship for rock glaciers. Using this relationship, we estimate a cumulative water volume equivalent of 48.03 Gt for the world's intact rock glaciers, 11.92 Gt for the western US, 0.99 Gt for the State of Utah, and 0.08 Gt for the Wasatch Mountain Range.

The Bryce Canyon 7.5' quadrangle is centered on the Paunsaugunt Plateau in the High Plateaus subsection of the Colorado Plateau physiographic province. The quadrangle encompasses the community of Bryce Canyon City, part of Bryce Canyon National Park (BCNP), and adjoining Dixie National Forest lands. The gently north-tilted surface of the Paunsaugunt Plateau sits at an average elevation of about 8000 feet (2400 m) and is drained northeastward by the East Fork Sevier River. Exposed bedrock in the Bryce Canyon quadrangle consists of a sequence of sedimentary rocks ranging in age from Late Cretaceous to Eocene. These rock units represent a 3500-foot (1065 m) section of fluvial, lacustrine, deltaic, and flood plain environments. Cretaceous Straight Cliffs, Wahweap, and Kaiparowits strata were deposited in fluvial and flood-plain environments along the western margin of the Late Cretaceous Western Interior Seaway. The Paleocene to Eocene Claron Formation was deposited in fluvial, floodplain, and lacustrine environments of an intermontane basin bounded by Laramide and Sevier uplifts. Claron strata typically weather to gently rolling hollows and hills. However, along the plateau’s eastern rim, rapid erosion of the Claron Formation by the Paria River system has sculpted steep-walled amphitheaters adorned with vertical spires, hoodoos, and slot canyons—collectively known as the Pink Cliffs that are showcased in BCNP. The Rubys Inn and Pine Hills thrust faults are major east-west-trending, mid-Tertiary (Neogene) thrust faults that bisect the quadrangle and define the margins of Emery and Johns Valleys (e.g., Lundin, 1989; Bowers, 1991; Davis, 1999; Biek et al., 2015; Davis and Pollock, 2024). The faults generally place Late Cretaceous strata onto the Paleogene pink member of the Claron Formation. Research over the past 35 years has shown that the Rubys Inn and Pine Hills thrust faults are part of the larger Paunsaugunt thrust fault system that developed in response to gravitational spreading of the Marysvale volcanic field about 20 to 30 million years ago (e.g., Nickelsen et al., 1992; Davis and Rowley, 1993; Merle et al., 1993; Davis, 1999; Biek et al., 2015; Davis and Pollock, 2024). Stream alluvium and terrace deposits of different ages are present along larger drainages, including the East Fork Sevier River. Alluvial pediment deposits blanket much of Emery and Johns Valleys.

Pleistocene glacial-interglacial climate variability led to cyclical expansion/contraction of the North American ice sheets with corresponding shifts in temperature and hydroclimate. While there is abundant information from the last glacial, there is much less information on prior glacial cycles, particularly from continental interiors. Long terrestrial climate records are important archives of temperature and rainfall changes associated with past climatic forcing, which can inform future projections about magnitudes and rates of change. Here, we revisit sediment cores drilled from Bear Lake (41.95°N, 111.31°W, 54.8 m) in 2000 as part of the Global Lakes Drilling (GLAD) project with microbial glycerol dialkyl glycerol tetraether (GDGT) techniques to reveal changing terrestrial climate over two glacial cycles. We find evidence for high salinity and lake stratification during the Holocene and Eemian, consistent with previous mineralogical and geochemical evidence for closed-basin, evaporative conditions. Branched GDGTs (brGDGT) temperatures for months above freezing averaged 5±1°C (1σ) for the last two glacial maxima (within MIS 2 and 6) and 7±2°C for the last two interglacials (Holocene and Eemian), with a deglacial warming of 5–6°C from the glacial maxima to the succeeding interglacial. The penultimate interglacial (MIS 7e) was 1°C cooler than the Holocene and Eemian, consistent with global evidence for a weaker interglacial. Glacial cooling estimates are consistent with local and regional proxy and modeling estimates. Long-duration 240 ka reconstructions from Bear Lake reveals the magnitude of lake temperature change encouraging investigation of contrasting dynamics and forcings beyond the last glacial period.

The Rill Creek 7.5ʹ quadrangle lies about 2.5 miles (4 km) northeast of the City of Moab, Utah. The map area encompasses the Sand Flats bedrock plateau between the salt-cored anticlines of Moab-Spanish Valley and Castle Valley. The northeast corner of the map includes a small part of the southwestern flank of the Castle Valley anticline. Small rivers and drainages in the region are connected to the larger Colorado River system. The Colorado River is located just northwest of the map area. Secondary tributaries of Grandstaff and Jackass Canyons flow west through the map area into the Colorado River. The prominent Grandstaff Canyon cuts east-west through the center of the map area and contains numerous popular trails for hikers and mountain bikers. These trails are key features of the popular Sand Flats Recreation Area that encompasses a significant part of the Sand Flats bedrock plateau. Sand Flats Recreation Area is famous for its slickrock off-roading and mountain bike trails. The recreation area covers most of the map area and is managed through a partnership between Grand County and the Bureau of Land Management.