Puncture Vine, Bull Thorn
Tribulus terrestris

Non-native, invasive, a nuisance weed because the fruits can puncture skin, hide, and rubber.
Difficult to eradicate, much agricultural land was abandoned.
Two species of weevils were introduced to eat the plants.

See UCR article:

Biological Control of Tribulus terrestris

Above: formation of fruits

Mature fruits - Photograph by Jack Kelly Clark, UCR