Rain + Dog Poop = Frogs?

I’ve spent the last three months going to the dog park at the end of my block at least 4 times a day, and I have not once seen a frog. However, this evening, when walking Chloe in the rain, I spotted my first Bay Area Poop Frog. The little guy was about 2 inches long, and much, much more afraid of me than of Chloe. She didn’t manage to eat him, but he gave her a pretty good chase.

Anyway, my question is “Has the frog been living in the park undiscovered for ‘lo these many months, or was he spontaneously generated when water hit the poop? Or possibly, did he migrate to the park on a raging gutter current?” I doubt the world will ever know.