Category: Geology and Caves

Southeast Idaho Geology and Caves

The three forces of nature that shaped this landscape to become mountains and valleys are the shifting of the land plates to push the mountains up, two major volcanic eruptions and finally the massive Bonneville Flood. Several rivers and streams ad their courses altered by these natural events, but virtually all the lakes and reservoirs came into being at the hand of man to fill the need for crop irrigation and electric power.

Map of Idaho Geology Looking at a geographic map of the United States people wonder how Idaho’s eastern and western boundaries were decided in such irregular pattern. The northern and southern borders of the state are nice and straight lines by contrast. The simple explanation is the western border used to be the coastline of the Pacific Ocean until California, Washington and Oregon rose up from the ocean floor pushing Idaho upward to become the western side of the Rocky Mountains. The highest point of the Rockies became the Continental Divide which is defined by where the snowmelt runoff from these mountains goes. This also explains the border of Idaho and Montana. Montana’s water runs southeast to the Missouri and Mississippi rivers to the Atlantic Ocean. Idaho’s water runs northwest to the Columbia River and the Pacific Ocean.

The Bear River is part of the westward flowing slope of the Rockies. It starts in the mountains of Utah and flows northwest to Idaho’s Bear Lake Valley and on to Soda Springs where it turns south through Preston and empties into the Great Salt Lake, which doesn’t make much sense. It travels over 400 miles to cover a distance of only 90 miles. It used to flow through Pocatello to the Snake River and onto the Pacific Ocean.

China Hat Volcano Geological Site near Soda Springs Idaho

Then a rift volcano, named China Hat, still visible near the intersection of state highway 34 and US 30 near Soda Springs raised the valley floor and sent a wall of molten lava 40 miles west to Pocatello. A second major flow occurred shortly after following the same path. These lava flows turned the Bear River southward. The remnants of these flows are spectacular to see at Grace, McCammon, Inkom and Pocatello.

The final event affecting the geography of Southeast Idaho occurred just 15,000 years ago. Prior to that a great deal of Utah and Nevada were covered by Lake Bonneville. What is now Preston was underwater but current day Downey was dry. Then at Red Rock Pass the natural dam broke and sent a wall of water estimated to be 300 feet high northwest all the way to the Pacific Ocean. The boulders pictured and the landscape of Marsh Valley were tumbled and polished by this event.

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Red Rock Pass

Red Rock Pass was cut through a sill of resistant Paleozoic shale, limestone, and dolomite, and forms a narrow gap two miles long. At one time the pass was at the shoreline of Pleistocene Lake Bonneville, 300 feet higher. Lava flows in the vicinity of Pocatello diverted the Bear River through Lake Thatcher into Lake Bonneville.

Minnetonka Cave

Tour through a wondrous half-mile of stalactites and stalagmites in the largest limestone cave in Idaho.

Caribou – Targhee National Forest

The Caribou National Forest was created in 1907 by President Theodore Roosevelt. Recently the administration was merged with the Targhee National Forest. Combined, the two forests now cover more than 2.8 million acres and thousands of miles of trails in southeastern and eastern Idaho, with small portions in Utah and…

Massacre Rocks State Park

Massacre Rocks State Park is one of the Historical Areas operated by the State of Idaho to remind visitors of the march of history through the state. Ten miles west of American Falls on I-86, take exit 28 and follow the signs. The park has stories to tell which date…

Soda Springs Geyser & Park

Soda Springs boasts having the world's only captive geyser. On November 30, 1937 in an attempt to find a hot water source for a local swimming pool, a well driller set free the natural geyser at a depth of 317 feet. It is located on Pyramid Spring, a travertine mound described by Fremont in his 1840s expeditions, along with other area springs.

China Hat Geological Site

China Hat and China Cap are rhyolite domes that formed around older volcano lava flows. There are many faults located in the area which have had a part in forming these land forms as well as multiple "grabens". This is also a great Bird Watching area. The best bird viewing…

Sulphur Springs

Sulphur Springs was noted in numerous early explorer and emigrant diaries. It was the first of several notable springs encountered in the Soda Springs area. When the wind is right, the distinct rotten egg odor can still be easily detected along Highway 30 east of town. The cold water and…

Tincup Canyon

This forested area offers public-lands-campground, recreation and wildlife viewing in the great outdoors of the Caribou-Targhee National Forest.

Octagon Park

Octagon Spring was a popular gathering place for local residents and for visitors to the famous Idanha Hotel,built in 1887,which was just across the street to the south of the spring.

Formation Springs Preserve

In 1989, 160-acres surrounding Formation Springs was turned into a preserve established by the Nature Conservancy to protect the crystal clear pools and unique wetland complex. The water feeding these terraced pools is very high in travertine (calcium carbonate), which has created a unique geology for the area, the most impressive…

Niter Ice Cave

The Cave was formed when basalt lava flowed out of a vent 500 thousand years ago forming a lava tube typical to this type of volcanic activity on the Snake River Plains. It was important to early settlers and native Americans for food storage. John A. Dalton, the original homesteader,…