About 30 miles north of Pocatello, Idaho, I-15 crosses the eastern edge of the broad, arc-shaped Snake River Plain and the tip of one of its voluminous lava fields. This little bit of interstately geologic heaven is known as Hells Half Acre. It is particularly noteworthy to me in light of the fact that I was on my way to Yellowstone National Park, situated as it is on top of undoubtedly the most famous magmatic hot spot on the planet. What is intriguing about Hell's Half Acre is that it sits smack on the track of the Yellowstone hot spot.
Massive volcanic activity has occurred in the Snake River Plain starting about 17 million years ago in the present Nevada-Idaho-Oregon border area. This activity is believed to have been caused by the Yellowstone hot spot. Volcanic features extend along the arc of the plain from this border area all the way to Yellowstone, many becoming younger towards the east. The Snake River Plain tracks this volcanic activity as the North American plate moves in a southwesterly direction at a rate of about an inch per year.
Track the hot spot here. This is so cool!
Further east along US highway 26 the Snake River drops down from the mountains of western Wyoming and into eastern Idaho. Here, it cuts a winding westerly swath through different layers of volcanic rock that do not track along the Snake River/Yellowstone hot spot path.