The tree is called Liquid Amber, or liquidambar styraciflua if Wikipedia's got it right. The pod is everywhere in so-Cal this time of year. You don't want your soft, bare foot to meet up with it. Boz navigates around these, carefully avoiding them with his delicate peds.
I saw a young woman gathering them the other day, and it triggered a memory from when I first moved here; I collected a batch and put them in a colorful bowl on the table in my apartment. To someone newly transplanted from Chicago, they were a fanciful arrangement in the sunny month of March.