On the northwestern edge of Redwood City, at the intersection of Edgewood and Cañada Roads, lies one outlet of the Crystal Springs Trail. Running parallel to Cañada Road, you can take this trail south towards Woodside, connecting with Runnymede as well as trails that will take you into Huddart Park (or take a well-deserved eating break at Buck’s, one of my faves).
Venturing north, in about 1.6 miles (tracked per my Garmin ForeRunner 310XT) you will come across the Pulgas Water Temple. The Temple was erected by the San Francisco Water Department as a monument to the 1934 completion of the Hetch Hetchy Aqueduct and is located at the aqueduct’s terminus. Go another 1 mile or so north, and you’ll come across the entrance to Sheep Camp Trail, from which you can take the trail into Belmont and Waterdog Lake Park. Or, from Pulgas Temple, go 3 miles or so north, and you’ll hit the intersection of Canada Rd. & Highway 92 (and from there, depending whether you’re biking or running, can continue on to get to Sawyer Camp Trail).
UPDATE: Ok, so apparently, per the SFPUC’s website, “Pulgas Water Temple will be closed to public access in 2011 due to SFPUC construction activities. All public access, including wedding ceremonies will not be allowed during 2011.” Also, there’s construction going on at the dam near Sawyer Camp, and the only way to access its entrance is to get to the Black Mountain Rd. exit off 280.