Looked at Dennis Paulson's pamphlet on the Dragonflies of Washington (1) and California dragonflies. Most Enallagma are more blue than black (civile, etc.). E. anna seems to be south of you and we would think the appendages would be much more obvious. E. clausum has a narrow, pinched thoracic black stripe. So we settled on E. carunculatum. Here is a photo (more mature and bluer than yours) and a scan which is closer to the color of your immature specimen. Yours is a male, by the way, can clearly see the secondary genitalia under the second abdominal segment. Whew! Had to work hard on that one!