This cicadellid was perched on leaves of Aralia californica, a California native plant in the Ginseng family (which also includes English Ivy, Hedera helix, a native of Europe and unfortunately a noxious and invasive weed in California --- widely dispersed into wild lands through bird droppings from human groundcover plantings). The Aralia was growing along a small brook in a coastal mountain forest of redwood (Sequoia sempervirens).

I'm almost certain this leafhooper is Pagaronia triunata, as suggested to me by Joyce Gross. It's nearly identical to the images of that species posted by Joyce, Jack, and Barry here on BugGuide, and identified by Andy Hamilton. And this specimen was photographed in the same general area as those others posts. But I'm placing it here because Cicadellidae is new to me, and I've found myself erroneously posting to species pages I thought I knew in the past.