After consultation with my non-resident geologist son and some pretty poor photos, he concluded that this formation came from magma, which is underground lava. It’s really frustrating to go to the USGS Rock Garden to try to follow their website list. Some of the rocks have empty plaques in front of them, some have plaques with a very different description on the website.
Conceding the lava cake photo to LeftyLaura (but I ate my fair share), here’s (formerly) lava
Sorry if it’s sideways. I forgot about the inability of technologies to play together nicely.
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