Moved from gall mites.

The only Eriophyids reported inhabiting Juniperus spp. berries in North America are four Trisetacus spp.: T. batonrougei(1), T. neoquadrisetus(1), T. ramosus(2), and T. quadrisetus(1). The image closely resembles the (same) illustrations of T. quadrisetus in these references. The regular rows of conical tubercles on the abdominal segments, the dorsal shield setae, and the shape of the portion of the rostrum drawn are distinctive. It is reported in nearby California, but I hesitate to identify it definitively as that species without the host species ID. J. occidentalis (Sierra Juniper) seems to be the species most heavily attacked by T. quadrisetus in California(3).

It would be very helpful if you could tell us what the juniper species is. I might be able to identify the mite species then, especially with such a detailed image.

This is an eriophyid mite... very distinctive. These guys often have an elaborate waxy coating that gives them an entirely different appearance. Preparing the specimen for SEM destroys this coating though, so the best images are with LTSEM. Cool find!