Marah fabacea (aka M. fabaceus)
My friend thought this was the dreaded cape ivy (Delairea odorata), because of the shape of the leaves and the viney way it was growing. It does look similar. However, I was pretty sure it was wild cucumber, but realized I never really paid close attention to either plant before. If I hadn't found the prickly fruit, I might have been convinced otherwise. Really, what do I know? I'm continually learning. There are 5 spp. of Marah found in CA, and the relatively flat corolla (rotate vs. cup-shaped) tells me this is M. fabacea. Btw, cape ivy has yellow flowers and shiny leaves.