Not necessarily. Manure piles ignite because of heat generated by decomposition causing straw or other bedding to reach its ignition temperature. From firsthand experience a damp, even wet pile with a lot of manure relative to the amount of dry material is most likely to catch fire. A day or two of rain can set up the right conditions. You probably don't see that kind of situation in Arizona.
You guys, of course, are correct. I keep forgetting how much wetter and humid almost everywhere is compared to Phoenix. Those types of environments just propagate gas-producing bacteria like crazy.