Lupinus arboreus (Yellow Bush aka Tree Lupine) was abundant in the sand dunes along the trail.
San Mateo County, California, US
(but still not entirely sure how to distinguish from, say, variicolor)
Lupinus arboreus, yellow bush lupine (USA) or tree lupin (UK), is a species of flowering plant in the legume family Fabaceae, native to California, where it is widely distributed among coastal scrub and sand dunes. Because it has been widely introduced, there is some uncertainty about its native range; it is thought to be native from Point Reyes National Seashore south to San Luis Obispo County.