Another gem of Santa Cruz mountains, the Henry Cowell State Park offers camping as well as day hike options. We did a 7.3 mile loop that took us through 4 river crossings, some waist deep.
We started at Rincon Fire road parking lot and followed the trail for 1.2 miles. The first river crossing comes here. Before crossing the river, you will see a sign for Diversion Dam trail. At this point cross the river and continue on Rincon fire road until you reach Big rock hole trail. At this point take right on to Big Rock hole trail.
This joins the Buckeye trail via a sandy beach river crossing (walk as far as you could before the trail ends at the river and then cross, even if you see earlier potential crossings. )
Third crossing is a bit tricky. There is a steep downhill (in 2017) to get to the bank to cross into a small island and then cross again to reach the trail head that starts going uphill for a good chunk before reaching the Rincon fire road again.
From the fire road we went in the direction of the observation deck (not much to observe), and continued on Rincon fire road until Diversion Dam trail and took right to stay on Diversion Dam where the 4th river cross happen.
The last river was the deepest at that time. It went to hip deep for me.
Diversion dam tail joins Rincon fire road again that leads to the parking lot.
Tons of fun crossing the river and the hike is best done in summer when the water level is low. Do call the rangers to check the water level before attempting.
Other useful links: http://www.parks.ca.gov/pages/546/files/henrycowellredwoodsfinalweblayout2013.pdf