Checking the CaliforniaHerps web site this appeared to be either Contia tenuis or Contia longicauda. The technical character for distinguishing the two species involves the length of the tail, as measured in the number of scales beyond the cloaca on the venter...which I didn't count or photograph. The brilliant red here seemed a better match with some of the CaliforniaHerps photos of C. tenuis. But when I asked naturalist friend Alice Abela what she thought, she replied that this species tends to get duller as they age, and the images of C. longicauda on the CaliforniaHerps web page seemed to mostly be older adults, whereas this looked to be a younger more colorful individual. Also, the coastal Santa Cruz County location and moist forest habitat clearly support Contia longicauda. Indeed the red pattern of the dorsum of the body, together with the black head, correspond well with images of C. longicauda here.

Both Contia species are said to feed primarily on slugs...and we saw an abundance of banana slugs throughout the day. Also, according to this informative web page (and others web sites), these snakes spend most their time under the duff or soil (i.e. they're fossorial), and this one was found scurrying across a paved road. I'm thinking we were lucky enough to see it because it wanted to cross the road, and so was forced to briefly travel exposed above ground.