Birch-Leaf Mountain-Mahogany (Cercocarpus betuloides var. betuloides)
https://www.inaturalist.org/observations/44698305 by @alex_bairstow
San Diego Mountain-Mahogany (Cercocarpus minutiflorus) https://www.inaturalist.org/observations/78168892 by @ekoberle

In fall, fruiting mountain-mahogany provides a picturesque display of curled, feathery styles extending from fruit and validates the genus name Cercocarpus which comes from the Greek for “tailed fruit.” These shrubs are not closely related to tropical mahogany trees, and they grow in lowlands, not just in mountains, so mountain-mahogany as a common name seems less apropos.

In San Diego County, Birch-Leaf Mountain Mahogany (Cercocarpus betuloides var. betuloides) is found from our upper foothills over the mountains and down the high desert slopes, while San Diego Mountain-Mahogany (C. minutiflorus) is found along the coast inland to the lower foothills. In the foothills where both species can be found, it is particularly important to note the characteristics that differentiate them.

Birch-Leaf Mountain-Mahogany by Alex Bairstow

San Diego Mountain-Mahogany by Eric Koberle
The leaves of San Diego Mountain-Mahogany are usually thinner, often cup-shaped, bright green, and the undersides have few, if any, hairs. The leaves of Birch-Leaf Mountain-Mahogany may be thicker and flatter, with gray pubescence. The flowers of San Diego Mountain-Mahogany may be smaller, and the style tends to be shorter than on Birch-Leaf Mountain-Mahogany.

Although the feathery styles of a Cercocarpus may make a pleasing photograph, it will be more helpful for an iNat observation if you focus instead on both sides of a leaf, showing the presence or absence of hairs.

See the San Diego County Plant Atlas website for more information about the plants of San Diego County.