This is Arizona's most recent lava flow. This particular volcanic flow is dated to between 1064 and 1065 A.D. As I travel around the state I find that many of the lava flows, even those much, much older, still look fresh and unweathered. I always wonder why none of the volcanic cones or lava flows are still active? Arizona is almost entirely seismically quiet. The only earthquakes are very small and are mostly centered in the extreme northern and western part of the state. It is interesting to speculate why.
Maybe it's just hard for us to think in terms of millions of years. A thousand years go by, and we feel like nothing is happening with our volcanoes. But a blowup every few thousand years would actually be fairly frequent (at least, this far inland).
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