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Great Salt Lake is the remnant of prehistoric Lake Bonneville, a vast freshwater lake that the U.S. Geological Survey describes as ten times larger than today’s Great Salt Lake. That is an approximate comparison, not an exact modern-area calculation: the present lake’s size changes with water level, and USGS does not specify a shared measurement date or whether the comparison is based on surface area or volume.
How Lake Bonneville became Great Salt Lake
Lake Bonneville occupied much of western Utah and extended into small parts of Idaho and Nevada during its most recent expansion, between about 23,000 and 12,000 years ago, according to the USGS overview. A USGS-authored geological review places the end of Lake Bonneville and the beginning of Great Salt Lake at approximately 13,000 years before present. These are broad geological dates, not a precise moment when one lake suddenly became the other.
As Lake Bonneville receded, Great Salt Lake remained as a smaller remnant in the Bonneville basin. The evidence does not support a highly precise, smooth reconstruction of lake levels throughout the period after Bonneville, so its changing extent is best described in approximate terms.
What “10 times its size” means
USGS describes prehistoric Lake Bonneville as ten times larger than Great Salt Lake. The agency does not state a measurement date or define whether “size” means surface area or volume, so the ratio should be read as a broad scale comparison rather than a precise calculation against the lake’s current footprint.
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For a dated point of comparison, the USGS overview reports that Great Salt Lake covered approximately 2,300 square miles at its 1986 high-water level. That is a historical measurement, not a current area; the lake’s footprint fluctuates with water level.
Why the modern lake is salty
Lake Bonneville was freshwater, while Great Salt Lake is saline in part because it sits in a closed basin with no outlet. Water can leave through evaporation, but dissolved salts remain behind. Over time, that process contributes to the saltiness of the remaining lake.
USGS describes Great Salt Lake as “the largest hydrographically closed lake in the Bonneville basin of northwestern Utah.” The description refers to a lake whose water has no river outlet carrying it beyond the basin.
Why Great Salt Lake was called America’s “Dead Sea”
“America’s Dead Sea” is a historical nickname, not a formal scientific name. A peer-reviewed review of Great Salt Lake’s microbial life explains that people once considered the lake sterile, helping give rise to the label. The nickname does not mean the lake is lifeless: researchers have documented bacteria, archaea, algae, and protozoa living in its brine.
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Sources
- U.S. Geological Survey, Great Salt Lake overview (2021), for Lake Bonneville’s freshwater status, approximate size comparison, expansion dates, and the 1986 high-water area.
- Oviatt, Atwood, and Thompson, USGS Publications Warehouse (2021), for the approximate transition date, the closed-basin description, and limits on reconstructing post-Bonneville lake levels.
- Peer-reviewed review of Great Salt Lake microbial life (2018), for the historical nickname and evidence of microscopic life.
- USGS report on Great Salt Lake’s closed basin, for the relationship between evaporation and salt retention.
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