One of my favorite things about Arizona is its geologic history. Northern AZ is littered with extinct volcanoes. Technically, AZ still has some active volcanoes, but I just read that they tend to go off every 10,000 years and the most recent one was 1,000 years ago, so we're safe for awhile.
Here's a lonely song to match the landscape: https://www.youtube.com/watch?v=sBtTufA-mNY
Oh, and SP in SP Crater means....sh*t pot. This is sh*t pot crater. http://en.wikipedia.org/wiki/S_P_Crater
Love the bleak lunar terrain in your pic.