Mexican Poppy (Eschscholtzia californica)
This brilliant yellow-to-orange flower (with some varieties showing peripheral white, see below) blooms from late January to May in our area, depending on seasonal warmth (and of course on winter rains). An annual that grows to 16" high, the Mexican Poppy has "fernlike, pale bluish green" leaves, "to 2 1/2" long (Epple, cited on main wildflower page, p. 75), and it appears in a wide variety of habitats. The flower remains open only in full sunlight.
Some years, after good spring rains, it bursts into such spectacular blooms that it fills whole hillsides, like this moment below on May 12, 2005 near milepost 8 on the Cascabel Road:
A pure yellow-to-orange color, as in the Mexican poppies shown below left, is by far the most common, but occasionally one sees them with peripheral white in color, as below right. Both of these were photographed in a single location along lower Hot Springs Canyon Wash on March 20, 2008. Click on each image for one of much better quality.