One of about a dozen vernal pools in the Rocky Peak area. More than just a puddle, these rainy season pools form as a result of the area's unique geology.
In my experience, excessive rainfall is not necessary for the pools to form. Normal month-to-month seasonal precipitation is usually sufficient. Their persistence depends on several factors, but in a season with normal to above average precipitation, the pools can last for several months.
From Wednesday's run on Rocky Peak.
Related post: Vernal Pool at China Flat