Hillside Springs group at the margin of the Summit Lake post-caldera rhyolite lava flow in Upper Geyser Basin, Yellowstone National Park

Hillside Springs group at the margin of the Summit Lake post-caldera rhyolite lava flow (the looming cliff) in Upper Geyser Basin, Yellowstone National Park.  In the past few thousand years, the springs have occasionally deposited travertine, which can be found at the bottom of the hill below the active springs. This travertine, which is not being deposited today, is evidence that the climate was wetter off and on during the past 15,000 years, because travertine deposition within Yellowstone caldera correlates with periods of wetter climate.