Photo by M. Gocke, USDA, Wikimedia Commons
Last week (“Trip to Seattle: Part 1”) I wrote about our drive over the “hump” of the Rockies in southern Wyoming and the drop down into the western plains. All along the road we saw clusters of cattle and also several, small herds of pronghorns scattered across the snowy, sagebrush plains. As someone once pointed out, they are more pronghorns in Wyoming than people! In fact, there are thirty-one cities in the United States that have larger populations than the entire state of Wyoming! None of those cities, though, elect two senators to serve in Congress!
Pronghorn fence. Photo by D. Sillman
There were lines of wooden snow fencing arrayed on either side of the Interstate. Without these fences, according to the Wyoming Department of Transportation (WYDOT), I-80 would be blocked most of the winter by blowing snow and deep drifts. In addition to the snow fences, there were also some very high, well re-enforced wood and wire fences that formed a barrier between the expansive rangeland on either side of the road and the highway. These fences were twice as high as typical cattle fences and were constructed with a wire mesh all the way down to the ground. We speculated that these fences might be designed to keep something enclosed that was much larger or much more agile than cattle. We didn’t think that anyone was keeping herds of bison (or herds of something even bigger or more exotic!) out on these remote, dry grasslands, so we decided that these fences must be designed to keep pronghorns off of the Interstate!
As I noted last week, pronghorns can run at amazing speeds (possibly 65 mph in a sprint!) but are not able to jump all that well. These fences, apparently were designed to be quite visible to a fast moving pronghorn and tall enough to discourage any attempt the pronghorn might have to try to jump over it. They were also built to be a dense enough barrier at ground level to prevent the running pronghorns from ducking under strands of fence wire. An article published by WYDOT described Wyoming’s use of these fences to funnel pronghorns away from dangerous sections of highway and toward safe passage “bridges” over the busy roads. We didn’t see any of the “pronghorn overpasses,” but they must have been there along the Interstate.
Photo by D. Sillman
We saw lots of mining and oil and gas extraction activity on either side of the Interstate all across southern Wyoming. The sagebrush steppe is, in itself, pretty empty looking and monochromatically brown. The mining and drilling operations, though, with their deep cuts into the underlying rocks, their piles of debris and their networks of dusty truck-ways and above ground tanks and pumping equipment beat the landscape down even further. Southern Wyoming is a very tired looking and a very heavily used place.
Photo by D. Sillman
The drive went past miles and miles of very dry grassland. There were sculpted sandstone mountains, and numerous wind turbines spinning away on the ridges. Wind is a major force in this environment! We didn’t see any trees until we were close to the Utah border and came across isolated clusters of evenly aged aspens tucked into the SE faces of the sandy hills. I assume that down in these sheltered spaces the trees were protected from the wind and were able to find and retain enough moisture for growth.
At the Utah border we dropped down enough in elevation to begin to see shrubs and small trees. Junipers grew in clusters at first in protected low spots in the terrain, but then spread out along the rims and ridges of the hillsides. There may be some pinyon pines mixed in with the junipers, but racing past at 80 mpg made it difficult to identify the exact flora around us!
Photo by D. Sillman
The landscape changed significantly when we get to Utah and entered the eastern edge of the Great Basin. We drove through and past low rolling hills that were covered with sagebrush and juniper. The soils were a deep red-orange that contrasted very pleasantly with the dark greens of the junipers. It occured to me that these colors were very close to being Chevreul’s color wheel opposites. They made the surfaces of the hillsides leap out to our passing eyes. Tall, orange-red cliffs loomed over deep, dark, shady canyons, all lined and highlighted by a border of dark green, junipers. Such a stunningly beautiful landscape!
Years ago I read John McPhee’s book Basin and Range which went into great detail describing the landscape and the causative geology of the “basin and range” topography of the Great Basin. I have to admit, I never fully saw what McPhee was trying to describe. That changed, though, as we drove through Utah and Idaho.
Photo by D. Sillman
Short, isolated, north-south running mountain ranges were scattered across vast, flat plains. We drove along on the flat in between the mountains and looked up at their pine-covered slopes and snow-covered peaks. Up ahead, there was always a next range hovering in the distance! Range after range, flatland after flatland: miles and miles of dry, brown sagebrush often irrigated into agricultural fields all punctuated by the deep green of the low junipers and the high growing mountain pines.
The last city in Wyoming was Evanston (elevation 6749′), and it represented the western edge of Wyoming Plateau. From there we drove through a pass in the Wasatch Mountains (which are recognized as the western edge of the Rockies) and headed down into the Great Basin. The road ran through Ogden Utah (elevation 4300’), then on to Brigham City (4436’,) Tremonton (4324’) and Snowville, Utah (4547’). We were on a broad, fairly even landscape heading north.
Off to our west was the Great Salt Lake. We got glimpses of the northeastern extension of the lake when the gaps in the median barrier matched up with low areas in the western hills. Deborah got out her phone to take a picture, but that sealed the deal: nothing but high unbroken hills after that! No clear view of the lake!
Shorelines of Lake Bonneville. Photo by Utah Geological Survey
We drove out of the deep, U-shaped canyon and left the Wasatch Mountains behind and entered a wide basin. This is the old lake bed of Lake Bonneville. The Great Salt Lake is but a remnant of this ancient lake. Shoreline markings are visible high up on the rocks around us and behind us. Ledges and pale lines of deposition mark the different levels of the lake. The surface of the Interstate would have been more than a hundred feet under water when Lake Bonneville was at its height!
Lake Bonneville was a lake of the late Pleistocene. It formed in stages between 13,000 and 30,000 years ago. It was, like the Great Salt Lake, a pluvial lake set in an isolated basin. The water that flowed into the lake from its broad watershed did not go on to any ocean, but instead it stayed in the lake until it evaporated or until, as in the case of Lake Bonneville, some calamitous event released it! Through most of its existence Lake Bonneville expanded and regressed at the mercy of climate. Cool, wet climatic periods caused the lake to expand and deepen, and warm, dry climatic periods caused the lake to shrink.
Map by Staplini, Wikimedia Commons
Lake Bonneville once spread out over 20,000 square miles and covered most of western Utah and parts of southern Idaho and eastern Nevada. It was in its maximum conformation, about 18,000 years ago, 980 feet deep with its northern-most shoreline in southern Idaho abutting a great mass of alluvial debris. The lake waters began to flow over low spots in this alluvium and, remarkably quickly, broke through the enclosing dam of rocks and sediments. A major part of this breech was in the present day Red Rock Pass in southeastern Idaho. The resulting flood was incredible!
Lake Bonneville emptied over half of its considerable water volume out through the Red Rock Pass and into the Snake River (and then into the Columbia River and out to the Pacific Ocean). The great flood lasted for about a year. Flow rates through the pass are estimated to be between 15,000,000 and 35,000,000 cubic feet of water per second! For comparison, the largest river on Earth (the Amazon) has an average flow rate of 7,000,000 cubic feet of water per second and a maximum flood flow rate of 12,000,000 cubic feet of water per second! The “Great Bonneville Flood” represented water flows that were the equivalent of multiple Amazon Rivers roaring down the canyon of the Snake River!
After the year of flood, the depth of Lake Bonneville was reduced to 430 feet (about 43% of its starting depth). It then persisted at this depth for the next 3000 years, eventually resuming its pluvial existence, rising and falling in response to cool and dry climatic cycles. The lake shrunk down to the present day conformation of the Great Salt Lake about 13,000 years ago, and, by convention, is referred to as the “Great Salt Lake” from that point on.
Next week: up on the Snake River Plain!
Bill, your articles are always interesting! Are the Bonneville Salt Flats located on old Lake Bonneville? Could you please change my address to arwicks66@gmail.com? Thanks! Hope you and Deborah are doing well 😊