Found in Los Angeles need help identifying, thanks!
This is a pinnately compound leaf, with the center leaflet larger than the ones along the side of the rachis.
There are many trees with this sort of leaf pattern, but the most common ones could be:
Fraxinus, Ash. Leaves will be opposite. At this time of the year I would expect some sign of flowers or young fruit. Ash usually have a very distinct pattern on the stems where branches have fallen off.
Juglans or related. Walnut, pecan, butternut, hickory and similar. Alternate leaves. This plant family has distinct leaf scars, where old leaves fall off.
More pictures that include trunk, bark, overall shape, flowers, fruit, and any other details can help.
Twigs with leaves still on showing 2 or more leaves so we can see if they are alternate or opposite can sure help. This will also show if the young growth has lenticels, and how many.
Look on the ground under the plant for old fruit. Fruit from the walnut family does not decay very fast, though they could be eaten or carried away by squirrels.