Would like to know what this hawk is. Ground in So Cal
It is most likely a Red-tailed Hawk (Buteo jamaicensis). This is consistent with your location and the general markings on the bird:
The primary feathers are dark on the tips. There are "commas" (dark comma-shaped markings at the base of the primary feathers just under the alula). The patagial area is dark. There is a mottled/dark "belly band." You can sometimes use the "dark head, light crop, dark belly band" to identify Red-tailed Hawks when passing perched birds quickly and you have little other useful clues, such as the tail.
The bird's left leg looks somewhat unusual in this image, but I think this is due to having a bit of a strange posture in the moment. Buteos are not "booted", meaning the leg feathers end at the tarsus (analogous to your heel) which is the first joint above the toes. The right leg is sloping away from the camera position so it is not appearing to show the same length as the left leg.
There's a useful quick guide at Hawk Migration Association of North America that has this guide:
Affiliation disclosure: I am an active volunteer of Hawkwatch International.