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The Los Angeles Basin province extends from the base of the San Gabriel and Santa Monica Mountains (part of the Transverse Ranges province) to the north to the base of the Santa Ana Mountains and the San Joaquin Hills on the south. In a geologic context, it can be pictured as a huge, deeply folded basin filled to a depth of up to 7 miles by some volcanic material and land-laid sediments, but mostly by sediments of marine origin—sand and mud deposited on the ocean bottom from 80 million years ago to as recently as 1 million years ago.

The Los Angeles Basin area has experienced uplift during the past 1–2 million years, and as this took place, the surface of the basin accumulated a layer of terrestrial sediment shed from the surrounding hills and mountains. The basin, in fact, would still be filling up with sediment were it not for the flood-control dams and channeled riverbeds that have largely replaced the original meandering Santa Ana, San Gabriel, and Los Angeles Rivers.

Cloud-walking, Laguna Bowl Road (see ssss1)