Hello,

That looks like a running crab spider, Philodromus sp. (Philodromidae).

These are harmless spiders.

The following was modified from the Field Guide to the Spiders of California and the Pacific Coast States by Richard Adams.

Philodromus are most common in herbaceous foliage and woody scrub but can also be found on the ground. They are also commonly found in homes and other structures in the spring of the year. Like other running crab spiders, Philodromus are able to move rapidly when hunting, they also often take a site-and-wait ambush approach.  They are mainly tactile and visual hunters, triggered by the movement of their prey. Resting on a twig with their fore legs spread open, a Philodromus will grab any insect that touches it or walks nearby.  Once a prey item is captured, the spider rapidly scoops it in with its fore legs and bites it, delivering a mix of venom and digestive fluids.  Philodromus neither wrap their prey in silk or crush it, but feed on it whole, sucking the prey’s liquefied remains through the bite wound. 

When a male Philodromus finds a female, he normally begins courtship by steadily tapping the substrate, a signal that tells the female that he is a courting male and not necessarily prey.  If she allows him to approach, he taps her on her legs and abdomen until he is in a position where mating can occur.  A Philodromus egg sac consists of a single sheet of silk sheet below the eggs and two slightly separated sheets above.  Once Philodromus spiderlings emerge from their egg sac, they climb to the tips of nearby twigs and balloon away on a silk strand.

Regards,

Howard