I don’t claim to be a poppy expert, but according to my wildflower guide for this area authored by Marianne Skov Jenson, she says, “Mexican Poppy - 5 to 12 inches. Flowers to 1 1/2 inches. Native. With rain at the right times they can blanket open areas. California Poppy is not native but can be found in landscaping and revegetated areas.”
I did a quick search and came across this site:
https://www.wildflower.org/plants/result.php?id_plant=ESCAM
Regarding the differences between the California Poppy and Mexican Poppy, it says, “Once considered a separate species, Mexican Gold Poppy is now recognized as a desert-inhabiting subspecies of California Poppy (E. californica). The two subspecies are exceedingly similar, one consistent difference being that the first leaves on seedlings of Mexican Gold Poppy are linear and undivided, whereas on seedlings of California Poppy they are divided in a Y-shape (a difference learned by careful greenhouse study).”