Landscape & Geology

The Yellowstone and Grand Teton region is one of the most dynamic seismic areas in the world -- wracked by earthquakes, cracked by water boiling to the surface, and littered with the detritus of previous volcanic eruptions. Today, the bowels of the Yellowstone caldera are again filling with magma. Geologic studies show that, for the last 2 million years, the plateau has blown its top every 600,000 years or so -- and the last explosion was about 600,000 years ago. That means that a titanic blow -- bigger than anything seen in recorded history -- could happen, well, any century now, give or take 10,000 years. The geological time frame is a long one, by human standards.

As you'll learn when you visit the exhibits on the park's geology at Moose, Mammoth, and the various geothermal areas, what you see on the surface -- great layers of ash and the core of volcanic vents, such as Mount Washburn and Bunsen Peak -- is only a fraction of the story of Yellowstone and Grand Teton.

Situated on 2.2 million acres, Yellowstone is significantly larger than its sister to the south. Encompassing 3,472 square miles, Yellowstone boasts 370 miles of paved roads and 1,200 miles of trails, and it is home to more geysers and hot springs than the combined total in the rest of the world.

Although it can't match Yellowstone's size, Grand Teton National Park is nothing to sneeze at. It has towering mountain spires, that have been compared to cathedral towers, reaching almost 14,000 feet skyward, picturesque glacial lakes, and a great deal of interesting topography. The 485 square miles of Grand Teton contain about 160 miles of paved roads and over 250 miles of hiking trails.

The Spires of Grand Teton National Park

Your first sight of the towering spires of the Cathedral Group -- the trois tetons (three breasts), as lonesome French trappers called them -- will create an indelible impression. A bit of history makes them even more interesting.

Their formation began more than 2.5 billion years ago when sand and volcanic debris settled in an ancient ocean that covered this entire area. Scientists estimate that roughly 40 million to 80 million years ago, a compression of the Earth's surface caused an uplift of the entire Rocky Mountain chain from Mexico to Canada. This was just the first step in an ongoing series of events that included several periods during which a miles-thick crust of ice covered the area. Then, 6 million to 9 million years ago, the shifting of the earth's plates caused movement along the north-south Teton fault that produced a tremendous uplift. The valley floor also dropped precipitously, and these simultaneous forces pushed the rock that is now the Teton Range to its present site from a position 20,000 to 30,000 feet below what is today the floor of Jackson Hole.

The west block of rock tipped upward to create the Teton Range, and the eastern block swung downward to form the valley that is now called Jackson Hole -- kind of like a pair of horizontal swinging doors that moved the earth 5 miles.

At this conclusion of the upheaval, and after eons of erosion and glacier activity, the Grand Teton peak, centerpiece of this 40-mile-long fault area, towered 13,770 feet above sea level, more than a mile above the visitor center at Moose Junction. Eleven other peaks over 12,000 feet high are in the park today, with conditions that support mountain glaciers. As you gaze upward at this magnificent range, you will notice that many of the cliffs are more than half a mile in height.

During geologic explorations of Mount Moran (elevation 12,605 ft.), which gets less attention than it deserves, it was discovered that erosion has removed some 3,000 feet of material from its summit, so it once must have been more than 15,000 feet high. Equally remarkable is the fact that the thin layer of Flathead sandstone on the top of this peak is found in the valley below, buried at least 24,000 feet below the surface -- further evidence of the skyward thrust of the mountains.

Although this is the youngest range in the Rockies -- yet another geologic anomaly -- the rocks here are some of the oldest in North America, consisting of granitic gneisses and schists, which are the hardest and least-porous rocks known to geologists.

The Teton area experienced a cooling trend about 150,000 years ago, during which time glaciers more than 2,000 feet thick flowed from higher elevations, and an ice sheet covered Jackson Hole. When it melted for the final time, some 60,000 to 80,000 years ago, it gouged the 386-foot-deep, 16-mile-long depression now known as Jackson Lake.

The receding layers of ice also left other calling cards. Several beautiful glacial lakes were created, including Phelps, Taggart, Bradley, Jenny, String, and Leigh. The sides of Cascade Canyon were polished by receding ice. Glacial lakes, called cirque lakes, were carved at the heads of canyons, and the peaks of the mountains were honed to their present jagged edges. Five glaciers have survived on Mount Moran. The best trail for glacial views is the Cascade Trail, which leads to the Schoolroom Glacier. But you shouldn't walk on the Mount Moran glaciers unless you are experienced; it's very dangerous.