Hendy Woods is a gem, and will always occupy a fond place in my memories. It was one of the first parks I discovered when I moved to the Bay Area 25 years ago, in the late 1990's. There are beautiful, old growth redwood groves from Big Sur through Humboldt county. IMO, Hendy Woods is the most beautiful Redwood grove closest to the Bay Area. It's not quite what you experience in Humboldt County, but it's about 100 miles closer (to where I live, at least) and it's a magical place.
This California State Park is located in the Anderson Valley, a historic agricultural area located in the Navarro river watershed. While only 120-ish miles from San Francisco, this area is remote. To get there, you've got to take Hwy 128 west from Cloverdale, which is right on the Sonoma/Mendocino border. This is a quintessential California windy road, which is either gorgeous or vomit inducing, depending on whether one is prone to motion sickness or not. It is possible to get in to the valley from the north, by taking Hwy 101 to Ukiah, and then taking Hwy 253 to Boonville. But this is "six of one, half dozen of the other" when compared to Hwy 128. You could also come in from the west, by taking Hwy 1 from any point south, but if you think Hwy 128 is too windy, Hwy 1 is even worse. For those towing trailers or driving an RV, I do not recommend trying to get to the Anderson Valley or Hendy Woods unless you're an experienced RV'er. Seriously - the drive in will not be fun, to say nothing about trying to park a trailer or RV larger than 25' (more on this later) in Hendy Woods. If you're new to RV'ing, get a pull-through spot at the Petaluma KOA and then drive your tow vehicle or tow-behind vehicle up to Hendy Woods for a day trip. It will take you about an hour to get there from Petaluma.
If you're not towing a trailer or in an RV, and/or car sickness isn't an issue for you or your family (as is my case), the drive in is really beautiful. You pass remote wineries and orchards, huge shady oaks, and the rolling hills that California is famous for. This is California country life at its absolute best.
Hendy Woods is about 7 miles west of Boonville, just past the tiny town of Philo. To enter the park, you make a left off Hwy 128 westbound. Another note to RV'ers: there is a one lane bridge over the Navarro river before the park entrance, so go slow and make sure the bridge is clear, so as to avoid having to back up. Boonville has a well stocked market and a gas station (that has diesel, for those RV'ers out there). It's a good place to stop and get supplies (read: beer, local wine, and ice) on the way in. There are a couple of restaurants in town, but this isn't Healdsburg. The wine tasting is awesome, but you won't be dining at a Michelin starred restaurant in Boonville after visiting the tasting rooms. You're much better off packing some prime cut ribeyes in your Yeti, buying a bottle of local red in town or at the winery, and grilling up steaks at your campsite in Hendy Woods. Again, California country living at its finest.
I would describe Hendy Woods as mostly a tent camping spot, but with a few spaces large enough to get a 25-28' foot trailer or RV into. But the difficulty level of getting an RV or trailer into Hendy is "black diamond." I took my 28' foot Airstream there, and I had to drive the road that circles the campground the wrong direction (per the advice of the ranger and the camp host) in order to get an angle where it was possible to jack my rig into the spot. Then, I had to make several fine tune adjustments to the precise location of my rig once in the spot, in order to get it as level as possible. Oh, and to level it, I had to perch one axle on a stump, while getting the other axle onto a leveling block. This is all standard stuff for experienced RV'ers, but since many people like to rent RV's and trailers now, I like to be very clear in my reviews about bringing larger equipment into a park.
I've camped in tents in Hendy, and most recently, in my Airstream. It's an amazing experience either way. The campground is in a huge grove of redwoods that keep it cool and filter the hot sun. In the wet months (sadly only about 2 months a year now), the Navarro river will be flowing, and you can walk to it from the campground. It's a great place to swim too if it happens to be running in the summer. There's at least a day's worth of hiking and exploring without having to leave Hendy. An ideal trip, for me, is 1 day in Hendy/Boonville, 1-2 days at the coast (about a 30 minute drive west on Hwy 128, not too many curves), 1 day wine tasting and swimming in the river. Hendy Woods is the perfect spot for this.
Hendy Woods is a magnificent place. With drought becoming such a problem in CA, and because I live in-state, in many ways I prefer camping in the winters now. I've not visited Hendy in the winter, but I plan to soon. Still, all the times I've been there in spring and summer, it hasn't disappointed. I always come home with a smile and a feeling of calm. Highly recommended. Per my rating system, I give this 5 stars because it's a place you should travel to specifically to visit. It's a must-have experience if you enjoy camping in the western part of the U.S.