ABSTRACT On this field trip we visit three sites in the Salt Lake Valley, Utah, USA, where we examine the geomorphology of the Bonneville shoreline, the history of glaciation in the Wasatch Range, and shorezone geomorphology of Great Salt Lake. Stop 1 is at Steep Mountain bench, adjacent to Point of the Mountain in the Traverse Mountains, where the Bonneville shoreline is well developed and we can examine geomorphic evidence for the behavior of Lake Bonneville at its highest levels. At Stop 2 at the mouths of Little Cottonwood and Bells Canyons in the Wasatch Range, we examine geochronologic and geomorphic evidence for the interaction of mountain glaciers with Lake Bonneville. At the Great Salt Lake at Stop 3, we can examine modern processes and evidence of the Holocene history of the lake, and appreciate how Lake Bonneville and Great Salt Lake are two end members of a long-lived lacustrine system in one of the tectonically generated basins of the Great Basin.

Weekly water samples collected in the spring and summer of 2012 demonstrate the dynamic geochemistry within the epikarst of an alpine karst aquifer in Timpanogos Cave National Monument in the Wasatch Mountains near Salt Lake City, Utah, USA. The results of chemical analysis of water from four cave pools, supplemented with concurrent samples from the American Fork River, suggest three modes of recharge: (1) diffuse recharge through the permeable matrix of the carbonate rock, (2) rapid recharge through open fractures in the epikarst, and (3) rapid recharge via piston flow through fractures occluded with colluvium. Water levels in the cave pools recharged by diffuse flow were very stable during the study period. Elevated dissolved solids characterized the geochemistry, including solutes associated with hydrothermal activity in this region (e.g., SO 4 2− and F − ). Isotopes of sulfur and carbon, along with cation-anion ratios suggest that sulfide oxidation may play some role in modern dissolution of the carbonate bedrock. In situ geochemical reactions influence the concentration of some solutes (e.g., HCO 3 − , Ca 2+ , F − ) and may cause a shift in the isotopes of dissolved inorganic carbon. Water levels in the cave pools characterized by rapid recharge, in comparison, were highly variable. When the flow path was direct, the geochemistry of the pool was strongly influenced by the timing and rate of recharge. During times of limited recharge, the geochemistry of these pools evolved toward the values of pools dominated by diffuse flow. On the other hand, when the flow path was impeded by colluvium, recharge was stored, and the geochemical signal was homogenized. In both cases, the source of recharge may be from elevations substantially above the cave pool.

Major-ion chemistry, strontium isotope ratios ( 87 Sr/ 86 Sr), stable isotope ratios (δ 18 O, δ 2 H), and tritium were analyzed for water samples from the southern Bear Lake Valley, Utah and Idaho, to characterize the types and distribution of groundwater sources and their relation to Bear Lake’s pre-diversion chemistry. Four ground-water types were identified: (1) Ca-Mg-HCO 3 water with 87 Sr/ 86 Sr values of ~0.71050 and modern tritium concentrations was found in the mountainous carbonate terrain of the Bear River Range. Magnesium (Mg) and bicarbonate (HCO 3 ) concentrations at Swan Creek Spring are discharge dependent and result from differential carbonate bedrock dissolution within the Bear River Range. (2) Cl-rich groundwater with elevated barium and strontium concentrations and 87 Sr/ 86 Sr values between 0.71021 and 0.71322 was found in the southwestern part of the valley. This groundwater discharges at several small, fault-controlled springs along the margin of the lake and contains solutes derived from the Wasatch Formation. (3) SO 4 -rich groundwater with 87 Sr/ 86 Sr values of ~0.70865, and lacking detectable tritium, discharges from two springs in the northeast quadrant of the study area and along the East Bear Lake fault. (4) Ca-Mg-HCO 3 -SO 4 -Cl water with 87 Sr/ 86 Sr values of ~0.71060 and sub-modern tritium concentrations discharges from several small springs emanating from the Wasatch Formation on the Bear Lake Plateau. The δ 18 O and δ 2 H values from springs and streams discharging in the Bear River Range fall along the Global Meteoric Water Line (GMWL), but are more negative at the southern end of the valley and at lower elevations. The δ 18 O and δ 2 H values from springs discharging on the Bear Lake Plateau plot on an evaporation line slightly below the GMWL. Stable isotope data suggest that precipitation falling in Bear Lake Valley is affected by orographic effects as storms pass over the Bear River Range, and by evaporation prior to recharging the Bear Lake Plateau aquifers. Approximately 99% of the solutes constituting Bear Lake’s pre-diversion chemistry were derived from stream discharge and shallow groundwater sources located within the Bear River Range. Lake-marginal springs exposed during the recent low lake levels and springs and streams draining the Bear Lake Plateau did not contribute significantly to the pre-diversion chemistry of Bear Lake.