What kind of spider is this
It is some kind of orb-weaver spider (Araneidae family) in either the genus Araneus or Neoscona. These are the types of spiders that make the large, geometrically patterned orb webs - "classic" spider webs.
All are completely harmless to humans.
Araneus gemma is one species that is common in the LA area. One can not identify the species from that photo, but some images of this species are at: https://bugguide.net/node/view/33683/bgimage