It's surprisingly difficult to find good astro sites in the general Santa Cruz area. Too many trees, too many areas already private or colonized. However, there's some possibilities, especially if willing to drive a bit.
Gray Whale Ranch meadow Elev 1120 ft = 342m. Where the bike trail crosses Empire Grade Rd. This is at 1200' elevation and is often above the fog. There's still light pollution from Santa Cruz, but not that bad. Beautful eastern horizon if you want to get dawn comets against the redwood trees. The biggest problem is that you cannot get off the road and there's plenty of headlights, even in the early morning.
Switchback Flat. Elev 1320 ft = 403m There's a little turnout on the west side of Empire Grade, midway through the switchbacks above the Smith Road intersection. It's got a decent north and western horizon, especially if you position yourself just right. Tough to get a low-clearance car over the hump, but you can park on Empire Grade and port your scope the last 100 feet.
Christmas Tree road. Elev 2594 ft = 792m. A few miles past the airport the road levels out at the 2400 ft elevation level and there is a large christmas tree farm along the right (east) side of Empire Grade. Towards the north end of this is an access dirt road going into the farm. There's room to park a couple of cars before you reach the locked gate. This spot has a great north and east horizon, poor southern, and mediocre western horizon.
Locatelli Meadow. Elev 2200 ft = 672m. If you want a good south and western horizon and little traffic, drive all the way to the end of Empire Grade, about 0.3 miles past Jamieson Creek road on your left will be a good size turnout which overlooks the Locatelli ranch in the big meadow there. Got some great shots of Comet T7 LINEAR here in the spring of '04. A few hundred yards further downhill is a dirt road with a locked gate; a couple of cars can park here and set up scopes with good horizons all around.
C.T. English / Loma Prieta School. Elev. 1700 ft = 519m. On Summit Rd between Santa Cruz and Los Gatos. There are various nooks/crannies on campus to observe from. Not the darkest place in the world, but it can be quite nice if fog covers the Silicon Valley. It's main draw is convenience for Karl and Tom and anyone living in this area. Requires a phone call from Karl to the guy who controls the on-campus lights.
Mt. Bache Road saddle. This is where Mt. Bache road crests the first ridge of the Santa Cruz Mtns and you get a view across the valley to Loma Prieta Peak itself. This site has a good horizon in the north, northwest, and northeast. We've used it for the many sunset lunar eclipses we seem to get over the past 10-20 years. It's not as dark as Bonny Doon, and it's a longer drive for those who live in the city, so we don't go here often. Drive up Old San Jose Road, turn right at Summit Road and go for another couple of miles to Mt. Bache Road (with sign) and switchback your way up the hill past the new millionaire mansions to the crest.
Fremont Peak. Elev. 2800ft = 855m. Not as good as the old days before Salinas auto mall and the major growth in Hollister, but still convenient and pretty dark, especially when there's fog below. Not quite as dark as sites farther south and east, like Mercey Hot Springs, Pinnacles, and Laguna Mtn, but it's close and still an excellent choice.
Laguna Mtn Camp. This is at 3,000 ft and near San Benito Mtn. It's a BLM campground and very dark skies in all directions. Darkest except perhaps for Big Sur, and a little closer/easier than Big Sur. It's also easier and darker than the Mercey Hot Springs site. Here's a .pdf of the Laguna Mtn area with campground and trails
Mercey Hot Springs. Elev. 2140 ft = 653m. A mile or so past Mercey Hot Springs look for BLM land and a dirt road heading up into the hills on your right. Drive up this another 5 miles or so to a big flat area on top of a ridge which has spectacular views in all directions. This was our site for the Astro 9 Fall '03 field trip. Here's a link to the hot springs website, which includes a larger scale map and directions. The north and east are marred by Central Valley lights, but it's very dark to the south and west. Barren and polluted with tons of spent gun shells by day, but views are great. No vegetation at all.
Chews Ridge. Elev. 5000 ft = 1527m. This is a bit of a drive, but some of the best skies in Central California. It's above all the haze of the marine layer, and on summer evenings looking south to the Milky Way there are no lights for literally 12,000 miles. The problem is finding a place to set up. At the ridge itself there's a parking lot you can use, but any traffic will raise clouds of dust. Not cool. If the MIRA people are at the Oliver Station observatory here, that gate might be open and you can drive up to the lookout, but you can't count on this. Otherwise, there are several turnouts and short fire breaks along Tassajara Road if you continue on beyond the ridge heading north. One is described here and shown here. But since the fires of early 2000's, the new trees have made it very tough to get a good view of the sky. I'd not recommend this one.
BackRanch Rd , pumphouse turnout. Elevation 500 ft. This is 7 miles up Hwy 1 along the coast. Look for an intersection sign at the community of Majors. On the left will be "Coast Road". On the right it's called Back Ranch Road at Mapquest and you'll know it because it goes underneath a big pipe which re-enters the hillside into which the road is carved. Back Ranch Road is a narrow, almost one lane pave road which winds uphill past a few farms and then by a new home to a little hollow and a pumphouse on the left. (In the daytime, you can see there's a nice little pond, apparently a former asphalt mine, on the right side of the road over the berm). Here there's space for a few cars to pull off and set up scopes. The sky to the west and south is very dark. East/Southeast you're looking towards Santa Cruz and it's a bit brighter, but overall it's a very dark site and easy to get to. Not good for foggy weather however; being only 500 feet elevation. Be prepared to get shoo'ed off by one cranky guy. About once out of every 5 visits this happens.
Highland Way, turnout. This spot has a panoramic view in all directions except north and northwest. It's close to Karl and the closest place to get above the fog from Cabrillo College. Drive up Old San Jose Road, turn right at Summit Rd, continue to the 3-way intersection with Mt.Bache Road and Spanish Trail Rd, continue on Highland Way to this spot. It's at 1900 ft and is usually fog-free. It's got a tree for shading from an overhead moon for a meteor storm... like the Aurigids '07!