As another reader also put it, "If it rains, it pours." And yes, when it rains, flooding happens fast.
Flash floods are common in Tucson and across Southern Arizona. If you see running water flowing across a road or trail, turn around.
In just the past week, Southern Arizona has seen three fatal accidents involving people either driving or going into fast-flowing washes.
It's not worth risking it, just find another route or wait it out. Most rain storms will pass in around 10-15 minutes.