The salt-encrusted wooden posts look like bleached bones sticking up through mud. The Great Salt Lake’s waters have retreated enough over the last two decades to expose a vast alkaline mud apron that stretches flatly across its southern shores. I tread lightly to avoid the same messy fate as two recent sightseers who left increasingly deeper footprints before wisely turning back.
But on this day, I am not so wise. I am here to experience the lake close and personal. I’m succeeding with my boots now entombed in sticky Great Salt Lake mud. To the north the lake’s waters are arrestingly still and covered by a light layer of mist that thickens with distance. Antelope Island looms eight miles to the northeast. Its façade throws a blurred reflection onto the surface, while the rest of the island fades abruptly into the mist.
Swearing that my feet now weigh 100 pounds each, I walk back toward a limestone protuberance that rises prominently more than 30 feet above the shore. After stomping my boots free of mud, I climb to its flat top and look westward. A southerly breeze carries the heavy scent of brine, and the sinking sun casts a warm light on the rock. You haven’t seen anything until you’ve experienced a Great Salt Lake sunset. And you haven’t truly experienced a Great Salt Lake sunset until you’ve observed one from atop Black Rock.
But there’s another facet that makes the view from here even more remarkable and unforgettable. It is as an abrupt contradiction with the serene lake surface below. I turn southward to scan the jagged flanks of the Oquirrh Mountains behind me. The bizarre collage of fractured ridges and wildly pitched slabs appear sculpted—as if they were violently chiseled by some prehistoric artist with a potent, methodical hammer.
This artwork is not only seen on the Oquirrh Range. Similar signs are everywhere across Tooele County: peculiar wave-cut formations high above the valley floors, articulated shorelines, and colossal sandbars. All of these are relics of ancient Lake Bonneville, the Great Salt Lake’s Pleistocene ancestor, which covered much of present-day Utah for tens of thousands of years. During its apogee it was 325 miles long, 135 miles wide and over 1,000 feet deep. At a staggering 20,000 square miles, it rivaled Lake Michigan in size—and for millennia kept much of Tooele County deeply hidden below its waves.
Lake Bonneville was named after French-born U.S. Army Capt. Benjamin L. E. Bonneville, who ironically spent little if any time in the area that would later bear his name. It was actually Joseph Walker, a fur trapper in Bonneville’s employ, who initiated the namesake. Walker named the salt flats for his boss while on assignment to explore the Great Salt Lake area in 1833. Geologist G.K. Gilbert—the man who studied and mapped the ancient lake and the earthen sink that held it—later applied the Bonneville name to the entire basin.
The basin itself is a major topographic depression that covers about 52,000 square miles of the Basin and Range physiographic province. Gilbert identified Lake Bonneville as the latest major incarnation in a 15 million year succession of dynamic lakes that occupied the Bonneville Basin.
Lake Bonneville is often described as ancient, a description that’s both apt and mildly deceiving—at least in regards to the geologic timeline. Most features in Utah trace their origins back millions and billions of years. Lake Bonneville was here only nine millenniums ago. In fact, it never completely disappeared. Aside from the extant Great Salt Lake, Lake Bonneville’s signature is prolifically etched throughout the eastern Great Basin. Its influence on Tooele County’s landscape is still seen, and felt, today.
Retracing Lake Bonneville’s past is a significant undertaking. While a 140-year collective effort has produced an impressive database on the lake, geologists concede that it’s a work in progress. Theories to evolve and to date the lake’s history continues to be refined as research progresses. One thing is for sure: it’s a fascinating story.
Lake Bonneville’s rise coincided with the latter stages of the last major Ice Age, beginning about 28,000 years ago. During that time, Utah’s air temperatures averaged 10 to 15 degrees Fahrenheit cooler than today. Mounting evidence shows that the Bonneville Basin’s climate was also wetter—in part due to lake effect precipitation. The diversion of the Pacific-bound Bear River into the Bonneville Basin by lava flows about 50,000 years ago is also believed to have caused the lake’s rise.
Less evaporation plus greater precipitation equals a steadily filling bathtub. The lake filled to approximately 300 feet above the Great Salt Lake’s present elevation and stabilized for 2,000 years, forming the Stansbury shoreline. This level is difficult to spot in the Tooele area but is visible on the Silver Island Mountains northeast of Wendover.
The lake rose again, peaking out at an elevation of 5,090 feet—the Bonneville level—at the basin’s upper rim, where it stayed for another 1,000 years. But something had to give, and give it did. About 14,500 years ago, the lake overflowed at the lowest point on the rim at Red Rock Pass just northwest of today’s Preston, Idaho. From there it spilled wildly into the Snake River drainage.
The volume of this flood exceeded all of the world’s rivers combined, according to Utah Geologic Survey Geologist Jim Davis. It tossed car-sized boulders as it gushed toward the Pacific Ocean. Davis says it may have taken all but a week for the outflow to scour the rim to bedrock and drain the lake 350 feet.
The lake then stabilized at the Provo Level for approximately 2,500 years. A warming trend and a drying climate drastically dropped the lake’s level. By about 11,000 years ago it had plummeted to the Gilbert Level, which is about 50 feet above the Great Salt Lake’s current height of 4,194 feet.
The ancient shorelines scoured onto area mountainsides look like multiple bathtub rings. Because of their height above valley floors throughout the county, it takes little imagination to envision what it may have looked like here during Lake Bonneville’s glory years. Picture the lake at the Bonneville level. Ocean-sized waves break on a steep gravel beach. The mountaintops look the same, but the summits are closer. That’s because they’re islands and island chains entirely surrounded by water.
The major ranges—the Oquirrhs and Stansburys—are peninsulas with lake fingers extending between them, completely covering Salt Lake, Tooele, and Skull Valleys. The expanse of water covering the Great Salt Lake Desert is virtually island-free. Imagine being an ancient mariner on a 100-mile crossing between Fish Springs National Wildlife Refuge and Hogup Islands near Lakeside.
Although Lake Bonneville before the breach at Red Rock Pass is a terminal lake with no topographical outlet, its relatively fresh waters teem with native Utah chub, least chub, specked dace, and Bonneville cutthroat trout. Various bird species thrive in marshes around the lake. Scan its shorelines and you’ll spot mammoths, musk oxen, buffalo, bears, and camels. Yes, camels.Fast forward to 2009. A satellite image from Google Earth clearly shows Lake Bonneville’s imprint—especially its western reaches. Beaches, spits, and deltas can be spotted on the modern topography. But the real tour of Lake Bonneville begins on the ground.
Among the lake’s most recognizable vestiges are the shorelines themselves. These terraced benches represent periods during which the lake’s level remained stable long enough for waves to deposit huge amounts of sand and gravel. Wave and algal action caused lime to precipitate on shoreline rocks, further enhancing the bathtub ring effect.
Just south of Tooele sits the Stockton Bar, a massive sandbar created when southbound Lake Bonneville currents deposited sediments in the 1.5-mile wide strait between South Mountain and the Oquirrhs. In geology circles, this 200-foot deep deposit is considered a “geoantiquity.” Its layered sediments provide a near continuous record of current patterns and coastal processes during the last Ice Age.
A less-visited feature is the Old River Bed at the southern end of Tooele County along the old Pony Express Trail. It’s a dry, clear-cut channel a mile wide (as broad as the Mississippi River at its confluence with the Missouri River). Dropping abruptly below the desert plain eight miles west of Simpson Springs, this ancient watercourse showcases the bizarre, larger-than-life character of many other Bonneville-era relics.
The Old River Bed was formed by drainage during post-Provo Level times. As Lake Bonneville shrank, water from Lake Gunnison in the Sevier Basin drained northward via a low channel into the Great Salt Lake Desert, carving a mile-wide, 100-foot deep gorge as it went. This river flowed for roughly 3,000 years as the Sevier Basin dried up.
An Overland stagecoach station was built in the dead center of the riverbed in 1862. The corridor posed several dangers for coaches and Pony Express riders. Although it’s wide and deep, it’s completely hidden from view until you’re right on its edge. Bandits or hostile Indians could easily ambush a rider as he popped into or out of the channel. Flash floods caused by heavy rainfall were also a threat. At least one flash flood was reported by a rider who narrowly escaped a 15-foot wall of water that washed out the trail.
To the northwest is the Bonneville Salt Flats, an expansive bleached-white playa that stretches over 30,000 acres near the Utah-Nevada border. The salt flats were formed as a receding Lake Bonneville deposited large concentrations of dissolved minerals on the exposed lakebed.
While the flats may appear unchanged from one year to the next, the crust slowly evolves with the seasons. Year-round ground water still flows to the salt flats and percolates upward. A shallow layer of this water accumulates on the surface during fall and winter, erasing scars and tire tracks as it flattens the saltpan. It then evaporates during spring and summer, leaving its minerals to supplement the crust.
The salt flats have an almost otherworldly appearance. The lack of normal visual cues on the flats confuses the human senses. It’s said that without intense concentration, it’s impossible for a person to walk a straight line on the featureless plain. This mind-bending topography has made the salt flats a favorite filming spot for numerous television commercials and movies. Automobile racers have flocked here for almost a century to test their speed machines on the hard, smooth crust.
From the primitive Desert Culture that left wooden tools in Wendover’s Danger Cave 10,000 years ago, to the modern gravel excavator, man has adapted to and exploited the Bonneville-crafted landscape. Terraces formed by the lake have become prime real estate along the Wasatch Front. Tooele City was built on a progressive Provo Level beach. Sediments deposited by Lake Bonneville are highly sought for wide use in construction due to their well rounded, well sorted, and unconsolidated qualities. Ongoing excavation of the Stockton Bar has raised concerns about its preservation.
Lake Bonneville’s principal legacy is the Great Salt Lake itself. Though it covers only 1/12 of the space that Lake Bonneville did, it’s still the largest salt lake in the western hemisphere and the fourth largest terminal lake in the world. It’s difficult to pinpoint exactly when the shrinking Lake Bonneville officially became the Great Salt Lake, but as it exists in the lowest areas in the Bonneville Basin, you might think of it in both figurative and literal senses as Lake Bonneville concentrate.
Salinity levels in the Great Salt Lake vary and are dependent on several environmental and geographical factors, but the Great Salt Lake is generally three to five times saltier than the ocean, making it uninhabitable to any form of life except the tiny brine shrimp.
There are about 4.5 to 4.9 billion tons of salt in the lake. It collects 2.2 million more every year from ground and surface water flow. On the lake’s southern shore, salt plants near Timpie and Grantsville use evaporative processes to produce varying grades of salt for human consumption, water softeners, and aircraft de-icing liquids. U.S. Magnesium pumps brine from the Great Salt Lake into solar evaporation ponds to produce magnesium and other chemicals. Together these industries annually extract about 2.5 million tons of salt and other minerals from the lake.
For sailing enthusiasts and stand up paddle surfers, the Great Salt Lake provides a taste of the sea. Its unique ecosystem attracts millions of ducks, shorebirds, and other water birds during annual migrations, and has been designated a Western Hemispheric Shorebird Reserve Network site. In this sense, the Great Salt Lake is less a “dead sea” and more a vibrant, evolving, life-giving kernel of its vast predecessor.
Back on my perch atop Black Rock, I analyze the ancient shorelines easily seen high on the northern flank of the Oquirrh Mountains. I realize that were I to stand in this same place 15,000 years ago, I’d never see daylight again. I’d be engulfed in pitch black, freezing water, nearly 1,000 feet below Lake Bonneville’s surface. Although I’m wearing a jacket in the here and now, the thought elicits tingles of cold fear on my skin.
In the fading light, I examine a well-developed stretch of the Provo shoreline midway up the Oquirrhs. The Stansbury Level is also visible just above Interstate 80, with traces of the Bonneville Level near the top of a central peak. The sun is setting now. It hangs just above a crescent dip created by the darkening flanks of Stansbury Island and the Stansbury Range to the west. As the sun drops toward the horizon, elongated water puddles on the playa vibrate with orange. Within minutes, however, their luminescence fades to steely gray and then black as the day’s last light evaporates from the sky.
As I climb down from Black Rock in the growing darkness, a sortie of seagulls glide quickly by, on some mysterious journey in the air their ancestors likely established at dusk thousands of years ago. I again stomp my boots to free any remaining mud before stepping inside my car to drive home. They call it “America’s Dead Sea.” But I’m thinking, how many more new namesakes must Lake Bonneville endure?