San Diego: An Introduction to the Region offers chapters on the geology, geography, history, and people of San Diego, each by an expert in the field.* "The First Residents" by Kenneth R. Martin offers information about the diet of the pre-European native population of the area. Here is a summary of the foods mentioned in that chapter, which I find very interesting.
Acorns, carefully prepared to leech out their toxins, were the staple food. Several species of oak trees provided the acorns, which were shelled, pounded in a mortar, and soaked or buried in the ground. The resulting acorn flour kept well; Indians used clay pots for making the flour into mush.
At least sixty plants were part of the Indians' diet. Yucca, chia seeds, prickly pear fruit, and beans from the mesquite were the most important. Thistles, wild oats, and various other cacti provided food. Several introduced plants -- filaree, wild mustard, watercress, and lamb's quarters -- grew and were used after the arrival of the Europeans. Indians also made medicinal teas.
Meat came principally from rabbits, chased down and caught in nets, or brought down by a throwing-stick. Indian hunters shot mule deer, mountain sheep, and antelope with bows and arrows, and also hunted quail, geese, roadrunners, mice, and other small mammals. To prepare the meat, Indian cooks pulverized the small mammals including the bones, and cooked them in clay pots. Deer and rabbit skins were important for clothing and blankets.
The seashore, marshes, and wetlands provided fish, shellfish, and salt. Indians fished with fiber nets and lines, and used shells to make fishhooks. Abalone, lobster, clams, octopus, and grunion were taken onshore and from canoes made from tule.
Two things strike me. First, the great variety of plant and animal foods and ingenuity of using plant fibers, clay pots, and so on for hunting and storing foods. Second, the extent to which much is no longer available, thanks to the large population now living in the area.
*I am reading the second edition pub. 1984, but plan to obtain the more recent 2004 edition.