Rained hard enough that a side canyon feeding into Antelope flashed briefly. Was interesting watching it happen. Water gradually pooling and trickling until critical mass reached, then it took-off. This small canyon was my egress into Antelope an hour before the flash. Served as reinforcement for the rain/slot/die connection. Something even the most naive of the Trek American group caught in this same canyon in 1997 should have been aware of.