As for the namesake of the park, the Organ Pipe Cactus, they aren't very pretty things, but they are unique here in the US. Southern Arizona is the far northern boundary for where they grow. They are primarily found in Mexico and love hot, dry conditions. They can't tolerate frost and grow well on south facing, rocky hills. At night, the rocks radiate warmth back to the cactus which helps them get through the handful of cold nights they have here. There are 26 species of cactus found here in the park.
Over the years a number of folks have come to try mining, ranching or farming and some were moderately successful, others not at all.
We have a number of folks who ask us about safety here on the Mexican border and I'll address that in another post as it is a BIG topic. But for now, I'll sit back, enjoy the beautiful sunset and plan tomorrow's hike.