JP found a soft spot in a board on the deck. Further probing revealed more soft wood and rot. Everything is made from cedar, but it seems like some cedar boards don't resist rot as well as others.
Both boys helped out. CP climbed under to pull out some lag screws, and GP learned how to drive in finish screws on the new steps.
The board that caps off the end of the steps is what gave out. It also took out a few inches of the ends of the top and bottom steps. We were able to trim the ends of the bottom steps and reuse them on the top. We only had to buy three pieces of wood (for $100).
We had perfect weather for a memorial day weekend, but it was HOT!