Spring season is probably the best time to visit Henry W. Coe State Park in the bay area for a dense blankets of wildflowers.
We did a 10.6 mile loop that went through China Hole.
The park is big enough to do hikes of pretty much any length.
First half of the hike had lot of shades on the trail we picked. But Henry Coe is known for open/unshaded trails that get really hot during the day time.
Trail Map can be found here: http://coepark.net/pineridgeassociation/documents/maps/western_zone/hq_hiking_map.pdf
We did go to the visitor center before starting and came to know there is water at Madrone camp ground for refilling. But that would be towards the end of the hike for us. So, took 3-liters/pp with us.
The hike itself is moderately strenuous. Most people can handle it. It’s the heat that can get to you. Plan ahead.
There were about 10 river crossings we had to do and at least half the time the water was deep enough, requiring shoes to be removed.
China hole area has sections for swimming. The water level is deep. We did take a dip before lunch.
Best part is the park is just an away from bay area.