The following information is from:  http://www.invasive.org/species/subject.cfm?sub=3937  Below is a summary (note the sentence in red!!!)

Scientific name: Tribulus terrestris L.  Synonym(s): bullhead, caltrop, goathead, Mexican sandbur, puncture vine, Texas sandbur

Puncture vine is an annual, low-spreading forb native to the Mediterranean [it is invasive in California and the US in general.]  Leaves are opposite, hairy, 1-3 in. (2.5-7.6 cm) long, and divided into 8-18 oblong leaflets. Flowering occurs from midsummer to frost, when 5-petaled, yellow, ½ in. (1.27 cm) wide flowers develop singly in the axils of the leaves. Fruit are circular, spiny burs that split into 5 sections. Burs can cause injury to bicycle tires, bare feet, and even small truck tires. Plants invade roadsides, pastures, fields and other disturbed areas. Plants are toxic to sheep and other grazers.  Here is a picture of the plant (click on the thumbnail for a better view.)

The best way to eradicate this plant is to pull it out by hand or cut it at the root with a knife.  Discard in a safe place otherwise the burs can still develop and plants will come back (the burs are actually the seed of this plant.)