Why Salt Lake City Has Giant Mountain Steps (Lake Bonneville Explained)

Lake Bonneville explained: Look up at the mountains above Salt Lake City. Those long flat steps running along the slopes are the old shorelines of Lake Bonneville, a lake that once covered much of western Utah. But if a lake left them, why are there several steps, and why are they no longer level? Who figured it out, and what do we still not know? This video follows the evidence: how a closed basin filled up, what G.K. Gilbert read in the mountains in the 1870s and 1890, the Bonneville Flood that dropped the lake, the lower steps that formed after it, and why the old shorelines tilted when the land rose. Where sources disagree (flood date, lake size, shoreline heights), the video says so instead of picking a number. CHAPTERS 0:00 The Staircase Above Salt Lake City 0:31 The Lake That Should Not Exist 1:32 A Lake With No Way Out 2:19 How a Shoreline Becomes a Step 3:15 The Man Who Read the Mountain 4:32 The Top Step 5:29 The Bonneville Flood 6:53 The Second Step 7:39 The Fall and the Step That Never Formed 9:00 Why the Shorelines Tilted 10:29 What We Do Not Know 11:43 The Answer #LakeBonneville #Geography #Geology SOURCES (some pages were checked only through summaries) Utah Geological Survey, "Commonly Asked Questions About Utah's Great Salt Lake & Lake Bonneville": https://geology.utah.gov/popular/grea... Utah Geological Survey, Public Information Series 39 (shorelines of Lake Bonneville): https://ugspub.nr.utah.gov/publicatio... Milligan and McDonald, Geological Society of America 2011 Rocky Mountain Section abstract (lake size, citing Oviatt and Miller 1997): https://gsa.confex.com/gsa/2011RM/web... Idaho State University, Digital Geology of Idaho, "Lake Bonneville flood": https://isu.edu/digitalgeologyidaho/b... USGS, "Computational fluid dynamics simulations of the Late Pleistocene Lake Bonneville flood": https://pubs.usgs.gov/publication/701... USGS Open-File Report 1961-0038 (isostatic rebound of the Bonneville shoreline): https://pubs.usgs.gov/of/1961/0038/re... G.K. Gilbert, "Lake Bonneville," USGS Monograph 1 (1890): https://pubs.usgs.gov/publication/m1 Utah Geological Association, Geology of the Intermountain West, article on Gilbert's 1890 interpretation: https://giw.utahgeology.org/index.php... Bonneville Shoreline Trail: https://www.bonnevilleshorelinetrail.... Wikipedia, "Lake Bonneville" and "Bonneville flood" (secondary): https://en.wikipedia.org/wiki/Lake_Bo... , https://en.wikipedia.org/wiki/Bonnevi... CREDITS AND DISCLOSURES Narration is an AI-generated (synthetic) voice (SonicVoice). The script was written by the channel from the sources above. Maps and graphics are drawn by the channel, schematic, not to scale; uncertain figures are marked as estimates. Photos and footage, CC BY (credit required; all on Wikimedia Commons except where noted): Marion Jensen, "Farmington Bench" (CC BY 3.0); Rick Willoughby, "Northern Utah Valley from the air" and "Salt Lake Valley From The Air" (CC BY 2.0); chadh, "Niagara of the West - Shoshone Falls ID 2007" (CC BY 2.0); Jayden Yun, "Antelope Island State Park, Utah" (CC BY 4.0); Pink Sherbet Photography, "White Rock, Buffalo Point, Antelope Island" (CC BY 2.0); Michael McConville, "Great Salt Lake at sunset" (CC BY 4.0); Russ, "Farmington bay to wastach mountains" (CC BY 2.0, Flickr via Commons); David Herrera, "Great Salt Lake and Interstate 80 from plane" (CC BY 2.0); pedrik, "Farmington Bay, Antelope Island and the Great Salt Lake" (CC BY 2.0); Shaun Fisher, "Sunset on the Great Salt Lake" (CC BY 2.0); r. nial bradshaw, "White Rock Bay, Great Salt Lake" (CC BY 2.0); video "Utah by Drone with the DJI Inspire 2 and Mavic Pro" by Jacob H (CC BY 3.0); video "Utah -- The Desert Paradise" by Bill Blevins (CC BY 3.0). Search each title on commons.wikimedia.org for the file page. Public-domain and CC0 material, via Wikimedia Commons: NASA (ISS photos, the Great Salt Lake time series), NOAA/CIRA, USGS, U.S. National Archives (NARA), BLM, the 1890 Gilbert monograph plates, C.R. Savage and W.H. Jackson 1870s photographs, and CC0 photos by Alfred Twu, Hermann Luyken, Brigitte Werner, Boluotou18, GoingsOn-YT, Marduk and OquirrhMountainMan. Some images illustrate similar landscapes, not the exact place described. Music: "Event Horizon" and "Red Shift" by The Grey Room / Density & Time, and sound effects, from the YouTube Audio Library. More geography explained from the evidence: subscribe to Terra Unusual:    / @terraunusual