The California Poppy (Eschscholzia californica) was selected as the State flower by the California State Floral Society, in December 1890. Other native flowers under consideration at the time were the Mariposa Lily (Calochortus), and Matilija Poppy (Romneya). The California Poppy though won the vote by a landslide. Eventually, in 1903, the California state legislature officially declared Eschscholzia californica as the State flower, and April 6th is designated as the official California Poppy Day.
California poppies are native to the west coast of North America, ranging from western Oregon to Baja California, and found in many open woodland, chaparral, foothill and grassland communities below 6,500 feet in elevation.
The genus, Eschscholzia, is named after an Estonian botanist Dr. Johann Friedrich Gustav von Eschscholtz (1793-1831) who was a surgeon and naturalist on Russian expeditions to the Pacific Coast of North America in 1816 and 1824.
There is some debate as to the number of native subspecies, but at least some taxonomists seem to accept that there are two primary subspecies, E. californica californica, consisting of four varieties (including the yellow and orange bi-color coastal form E. californica californica var. maritima that is commonly seen here along the Central Coast), and the yellow subspecies, E. californica mexicana, or Mexican Goldpoppy, of the Sonoran Desert. Numerous hybrid cultivars have also been produced by horticulturists in a wide range of colors and habits.
The varieties within the E. Californica californica subspecies show various subtle differences in color and habit. Along the coast, from the San Francisco peninsula northward, E. californica californica var. californica tends to grow more prostrate and has predominantly yellow flowers. In inland non-arid regions the orange flowered perennial form E. californica californica var. crocea predominates, and is taller in habit than E. California californica var. peninsularis which is found in more arid environments, and grows as an annual. When planting California Poppies within the State, it is recommended that the variety native to your region be sown.
Although Eschscholzia californica is native to western North America, it has reportedly naturalized in many parts of the world, including India, Chile, Argentina, Australia, and South Africa, and is even considered an invasive plant in some parts of the United States outside of its home range.
This year we only have a few California Poppies blooming here, in part because our gophers and deer seem to destroy them faster than they can grow or set seed.
In late winter to early spring, the leaves begin to emerge and are blue-green in color, and deeply dissected, growing from the base of the plant.
Flowers are borne on single stalks, appearing between February to September, with the heaviest bloom period through May.
At the base of the flower is the receptacle. This is a distinctive expanded rim that is most readily visible when the flowers are still in bud.
Above the receptacle there are two green fused sepals that enclose the flower bud. As the bud swells, and the petals unfurl, the sepals fall away.
The flower opens to reveal four overlapping yellow to orange petals forming the cup-shaped flower. The early Spanish explorers would call California Poppies copa de oro meaning ‘cup of gold’.
In the very center there are numerous stamens and two fused carpels.
The flowers are sunlight responsive, closing before sunset, and remain closed on overcast days.
After the flowers fade, 3-9 cm long seed pods are formed, containing 1.5-2 mm brown to black seeds, which are scattered in all directions when the pods open with explosive force. However, as the deer devoured these flowers shortly after they bloomed, I have no seed pods to show you, but the botanical print below illustrates them well.
The dehiscent nature of the seed pods means that timing is critical for collecting seeds from plants in the garden. Last year, as the pods turned brown, but before they split open, I simply placed the pods in a closed paper bag, so as the pods shattered, the seed was captured. The seed can then be sown, ideally in the fall, just before the winter rains return for bloom the following spring.
California Poppy flowers historically were predominantly pollinated by beetles, but now are visited regularly by European honey bees (Apis mellifera).
There are many documented uses of California Poppies by Native Americans. The Costanoans used a decoction of the flowers in their hair to kill lice, and they also laid flowers under the beds of children to aid their sleep. The Mendocino Indians used the juice of the roots as a wash for skins sores, and also consumed the juice for use as an emetic, or as a treatment for tuberculosis. Small pieces of root would be placed within a tooth cavity to treat a toothache. A number of tribes boiled or roasted the leaves as greens, including the Luiseno, and Neeshenam. The Cahuilla women reportedly used the pollen as a facial cosmetic. 
 Daniel E. Moerman’s Native American Ethnobotanical Database