Tiburon Uplands Natural Preserve

I found this place while running around Paradise Dr. and past this mysterious overgrown entrance to a hiking trail. Lo and behold I looked it up and saw that it was connected to Old St. Hilary’s Open Space Preserve. It has one official trail — The Loop Trail. It’s less than a mile and somewhat steep and entirely wooded. Take a left at the park bench at the top of the trail and take the unmarked trail to get to Old St. Hilary’s.
Its pretty cool, but not very scenic. I would just go to Old St. Hilary’s and call it a day. I’m not surprised that this the trail looks pretty overgrown.
Tiburon Uplands is a nature preserve, rather than a developed park. Its 24 wooded acres are tucked into a canyon along a quiet stretch of Paradise Drive near Tiburon, about one mile south of Paradise Beach Park. A short but strenuous one mile loop trail winds through mature woodlands and allows visitors to enjoy a variety of native plants and animals, as well as excellent bay views from higher elevations. The property adjoins the Old St. Hilary’s Open Space Preserve near the ridgeline. The preserve provides a secluded natural experience with few recreational facilities, and is not easily accessible. Dogs are allowed on leash.
Directions:
From Hwy 101 in Mill Valley, take exit 447 for Tiburon Blvd (Hwy 131) east 1.8 miles. Turn left onto Trestle Glen Blvd, right onto Paradise Dr, and follow for 1.5 miles. The park is on the left.

I access this trail about 7 miles up Paradise Drive from Main St. Tiburon, Ca. The trail is not marked well but you can see a marked wooden sign to the left and a «pull off area» to the right where you can park. The trail is beautiful! I recommend staying to the right on the way up, enjoying the scenic views of San Francisco from the top, and make your way down to the left. The trail is .07 of a mile up and .07 of a mile down– a great little hike to start a day off right, with a rewarding summit view! When you are hiking up you feel as though you are in the movie fern gully.

Pretty confident this is a different name for the St. Hilary Nature Preserve:

The narrow hiking-​only trail climbs moderately through woods with lots of bay views and to Golden Gate bridge. Most part of the trails are shady but the view at the very top is well worth it. Remember to glance towards your back every now and then as you are looking out to the East Bay as you climb. Breathtaking views to Angel Island as well and you can also see Bay Bridge and Golden Gate very clearly at the highest point.