Rattlesnake Crater east of Flagstaff is one of the more unusual volcanic features in the San Francisco Volcanic Field. This type of volcano is called a maar – a crater that forms when rising magma interacts with groundwater to produce very explosive steam blasts. A scientific paper describing a possible plumbing system at the Rattlesnake maar can be obtained at the link below. (1st of two posts for Rattlesnake Crater contributed by Wayne Ranney - (https://earthly-musings.blogspot.com/).)
FIGURE CAPTION: View to the west-northwest toward Rattlesnake maar. The San Francisco stratovolcano is in the far distance on the left (elev. 12,633 ft or 3850 m) and numerous scoria cones dot the rest of the landscape in the San Francisco Volcanic Field. Photo Credit: Dawn Kish.
Rattlesnake Crater is located on the Coconino National Forest and is accessed by dirt roads north of Winona off of Interstate 40. However, to obtain the all-encompassing and spectacular view shown in the first photo, park your vehicle where maar crater disappears on the left (and located where the dark juniper trees pinch out) and walk east along the top perimeter of the maar. At its eastern edge, make the steep climb (no trail) to the scoria cone that partially overlies the maar on its south side (second photo). Complete the loop by scampering down the west face of the cone and return to your vehicles.
Scientific paper on the formation of Rattlesnake Crater: https://www.researchgate.net/publication/282120025_Subsurface_structure_of_a_maar-diatreme_and_associated_tuff_ring_from_a_high-resolution_geophysical_survey_Rattlesnake_Crater_Arizona