[DoctorBulldog]

Solid rock subsidence crater (affectionately known as a "Retarc" (Crater spelled backwards)):



Not as pretty as Frenchman's Flats, but still easily measured.

Cheers!

[TXnMA]

“Retarc” — OK! I note it also has the characteristic “ring” and instrumentation lead-ins...

I’m assuming those two structures were built post-shot; otherwise, those guys really knew their business! ‘-)

BTW, we’re probably the only two freepers would consider referring to Frenchman’s Flats as “pretty”... LOL!