A brown one.
Found under a piece of wood,
The Pacific tree frog (Pseudacris regilla), also known as the Pacific chorus frog, has a range from the West Coast of the United States (from Northern California, Oregon, and Washington) to British Columbia, in Canada. They live from sea level to more than 10,000 feet in many types of habitats, reproducing in aquatic settings. They occur in shades of greens or browns and can change colors over periods of hours and weeks.