I recently was sitting under a huge oak tree and sketching with my friends Suhitasketch and Teaandmarmalade. At some point, Suhita pointed these beautiful caterpillars sitting on her sketchbook and soon I counted over a dozen on our table.
After a quick search, I found out that these beauties are Western Tussock Moth
They are actually pests and chew through a lot of oak tree leaves in the area. Stanford University is fighting them by releasing microscopic worms (predatory nematodes) and spined soldier beetles, as well as power-washing trees and surfaces where eggs are laid and cocoons are left.