From 280 go west on Page Mill Rd. From 101 go west on Oregon Expressway, it then becomes Page Mill Rd after El Camino. You enter the preserve by crossing the road. The trails are a mixture of singletrack and fireroads.
Some sections are pretty technical.
What they lack in quantity they make up for in quality. Watch out for rattlesnakes, I see them on the trails pretty regularly and if you're not paying attention it's easy to ride into them. LOTS of access points and trailheads. There's not alot of tree cover here either, but it is still as nice, fairly scenic ride. Roads are very popular with road cyclists.