Upper Falls of the Yellowstone River
A waterfall is a clue that you are standing on a geologic crossroads.
A waterfall forms in a river channel where harder rocks meet softer rocks that erode more easily and quickly. Here, volcanic and hydrothermal activity have created the 109-foot (33 m) Upper falls.
Why here?
1 About 480,000 years ago, lava formed a layer of rock that resists erosion. The lava naturally cracks in a zig-zag pattern.
2 Over time, hydrothermal springs rose through some of these cracks, altering and weakening the lava.
3 The Yellowstone River flowed through the zig-zag cracks and eroded its river channel. Once the river reached the softer, hydrothermally-altered rock, erosion increased and created the Upper Falls.
Marker can be reached from South Rim Drive 0.6 miles east of Grand Loop Road.
Courtesy hmdb.org
