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.
FIGURE CAPTION. View to the southeast toward the scoria cone where the first photo was taken. This scoria cone post-dates and partially buries Rattlesnake maar. In the near ground are steeply-dipping beds of welded tephra thrown out of the center of the maar (valley floor) during its eruption.
Rattlesnake Crater I and II are invited posts from Wayne Ranney (https://earthly-musings.blogspot.com/).
Online resource: 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