Great Basin Naturalist Memoirs


Utah Lake is a remnant of Lake Bonneville, from which it originated about 8,000 years ago. Analysis of sediment cores reveals significant variations in lake salinity and sedimentation rates. Notable examples are a very dry, high-salinity period between 5000 and 6000 years ago; a major freshening, wet period between 2700 and 3000 years ago; and a very dry, high-salinity period between 1400 and 2600 years ago, smaller variations are interspersed through the lake's history.
Long-term sedimentation rates are estimated at about 1 mm (0.039 in) per year in most of the lake, but post-colonization rates appear to be about 2 mm (0.079 in) per year. Faults in the lake appear to be lowering the lake bottom at about the same rate as sediment has been filling it. Bottom sediments consist of about 60 to 80 percent calcite in the lake proper, much of which precipitates from the lake water itself.
The lake-bed faults are similar in character to those of the Wasatch Fault that bound the valley and mountains a few miles to the east. Lake bottom springs and seeds are localized, in the most part, along the eastern and northern lake margins where all major tributaries occur and groundwater recharge is largest. Only limited spring activity appears to be associated with the faults.
In a geological sense, Utah is an old lake-shallow, turbid, and slightly saline-and has been since its "birth" with the demise of Lake Bonneville approximately 8,000 years ago.