Creating impressive billowing plumes in the cool early morning, these vents make a convenient drive-up photo op. Hot rocks below the surface boil rainwater as it percolates down, producing the steam. While the vents at the parking area are perfectly fine, even more evocative is Steaming Bluff, found along a short walk out to the rim. Here, curtains of steam frame the cliffs above a post-apocalyptic view, giving you the distinct feeling that something BIG happened here.