Henry Cowell State Park is a great place to be on a hot day. It typically has the coastal influence in its favor, even when the Santa Clara Valley Frying Pan is set to deep fry. And on the occasion when the ambient temperature is toasty, the shade of the redwoods brings the thermostat down several notches. HCSP is not particularly friendly to mountain biking, but one can craft a fairly fun 18km ride out of it with a little creativity.
HCSP is a small park--16 square kilometers--with an elevation range of 50m to 250m. It has 30km - 50km of trail (depending on who you talk to), but mountain bikes are limited to roughly 9km of that. There are only three trails (actually fire roads) open to mountain bikes: Pipeline, Ridge, and Rincon. Supposedly Powder Mill is open to bicycles, but all of the Powder Mill signs I saw had a nice bright red slash through the bicycle symbol. The negatives: Pipeline is an asphalt access road, 50% of Ridge is a powder sand quagmire, Rincon is out and back. There is only one route that makes much sense:
From the main parking lot, go up Pipeline.
This gets intensely steep in some sections (over 15%), but because it is on asphalt, 1:1 gearing will get you up it. After roughly 2km, just before Pipeline gets really steep,
take a right onto the Rincon Fire Road.
This goes up mostly rideable single-ish track for a km or so, then heads down to the San Lorenzo River. This is a fun 3km downhill that stops abruptly at the river. This is the low-point of the park: 50m. There is no bridge, and there isn't much trail on the other side of the river, so the best option is to cool your feet and eat a Z-Bar, then turn around and climb back out. Most of the climb out is rideable. The bottom part was recently graded (2009-05), so parts of it are too loose to ride, but generally it is a good, lung-busting ride.
Once back to Pipeline, hang a right
and gear down for the afore-mentioned 15% grade. This more or less levels out after 500m, at which point you come to the Ridge Trail junction. Do not ride this part of the Ridge Trail! Nearly all of it is deep, powdery sand that even 60mm tires won't float over. It also has water breaks that are unrideable and a brief section of unrideable redwood roots. To top it off, much of it is fully exposed to the sun, so on a toasty day you may well melt.
Continue on Pipeline for 2km until you get to the other side of Ridge Trail.
This part of Ridge Trail is rideable! It is a good climb of a km or so up to the observation deck. This is the high point in the park (250m), and the observation deck allows one to see to the ocean on a clear day, but there's not a lick of shade on the deck itself, so you may want to enjoy the view from below. There is a nice park bench in full-shade. There is also water available, but be forewarned: horses slobber all over the faucet trying to get their fair share. Yech! Once you're rested,