The sky is big and blue with gauzy clouds, and the hillsides populated with strange shapes of cacti and spiky grasses. This is the Organ Pipe Cactus National Monument near the border between Arizona and Mexico. I was struck by the harsh alien beauty. We camped three nights there, hiked, attended ranger talks at night, and learned lots about the cacti. The night was quiet and dark because of the distance from towns. Every campsite was bordered by its own large cactus.

At the end of our stay, I realized that I …