The California poppy, Eschscholzia californica, is the CA state flower. It grows everywhere this time of year, even in the tiny bit of soil next to a drainage grate, or in the sandbags lining a creek.
It is sometimes found next to dandelions or Bermuda Buttercup, another common but pretty yellow weed.
Every year, April 6 is California Poppy Day and May 13th – 18th is Poppy Week. I’m right in between the two with this post.