Mt Diablo: Fossil Ridge-Rock City-Sentinel Rock Trail Hike

Wednesday, August 31, 2016

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Mount Diablo State Park contains geological formations rich in fossil resources. Marine mollusks of Miocene age are abundant along the southern flank of the mountain. Fossil plant material is also common in this area. Along the southern boundary, 9 million year old river deposits have yielded a large number of vertebrate fossil fragments including sabre-tooth cats, mastodons, horses, camels, and llamas. *1

This hike climbs up from Mt Diablo South Gate Entrance on Summit Trail up to Fossil Ridge. Travel out and back along W Fossil Ridge and E Fossil Ridge before exploring the sandstone formations at Rock City. Explore Rock City! Features include the Wind Caves, Elephant Rock, Sentinel Rock, Artist Point and Fossil Ridge. Native American grinding rocks are located near Grotto. A great place to picnic. *3

Begin this trail hike from Mt Diablo Scenic Blvd, walk uphill to Mt Diablo State Park South Gate Entrance to the Summit Trail Trailhead.

Summit Trail begins from the south edge of the park as it winds up through the Black Hills towards Dan Cook Canyon. 

A trail for tree lovers and rock lovers, and a great favorite of mountain bikers. The environment varies from a dry oak savannah to a shady canyon of maples, sycamores, alders, and bay trees. *2

The trail comes to a bridge crossing to Green Valley Trail junction.

Turn right to stay on Summit Trail, it continues eastward along the shady canyon with moderate grades.

The trail opens up with views of the chaparral covered slopes around Pine Ridge.

Summit Trail continues to climb before exiting onto a paved road near Live Oak Campground.

Turn right and follow the road to W Fossil Ridge Rd junction.

Turn right onto W Fossil Ridge Rd, the trail travels westward up along the ridge for 0.7 mile. At Artist Point Trail junction, go straight to stay on W Fossil Ridge Rd.

The trail climbs up Fossil Ridge through the oaks and scattered pines with fabulous views of Sycamore and Green Valleys!

The trail levels out along the ridge to its high point at 1605 feet and a bit beyond.

Enjoy the stunning panoramic views!


Reverse your way back down from Fossil Ridge.

At Artist Point Trail junction, turn right and head uphill towards Artist Point. The trail cuts through the oak woodland to Holey Rock.

Walk around, explore Holey Rock and view the wonderful sandstone carvings!

Stay on the trail, it leads out to the picnic areas around Artist Point at 1680 feet.

Enjoy the rock formations and the wonderful views of Black Hills!

Follow the paved road down to the gate followed by an immediate right turn, it leads to the Uplands Picnic Area adjacent to South Gate Rd.

Go straight onto E Fossil Ridge Rd. Trail starts as small road, badly paved, climbing hill steeply; there is a simple gate and sign barring public vehicles. 

The initial climb opens up imposing vistas of the massive main peak of the mountain, as well as of San Ramon Valley in the opposite direction.

Continue along the ridge to its end. Fossil Ridge: Evidence of previous ocean residents is embedded in these rocks. Access from Rock City. Please leave them for future visitors to see. Blocks of these sandstones were quarried from this site to build the summit building in the 1930’s. *2

Follow the faint trail up to the top of the rocky ridge. The road parallels the crest of Fossil Ridge – the adventurous may wish to scramble up to the rocky ridge, a sharp hogback (tilted sandstone layer with adjacent layers eroded away) with interesting exposed fossils, rock-garden-like appearance. Dramatic view of Black Hawk Ridge strata across Sycamore Canyon from small path beyond end of road. Good bird watching. *4

Fossil Ridge: Evidence of previous ocean residents is embedded in these rocks. Access from Rock City. Please leave them for future visitors to see. Blocks of these sandstones were quarried from this site to build the summit building in the 1930’s. *2

U-turn and descend Fossil Ridge back to the Uplands Picnic Area.

Follow the paved road to Rock City Live Oak. Rock City: You’ll find unusually large sandstone formations and small caves here. Numerous picnic sites and campground. *2

Explore Rock City! Features include the Wind Caves, Elephant Rock, Sentinel Rock, Artist Point and Fossil Ridge. Native American grinding rocks are located near Grotto. A great place to picnic. *3

Explore the sandstone formations and etchings at Big Rock.

Elephant Rock & The Grotto.

Follow the Trail Through Time to the Wind Caves, sandstone formations carved by wind, rain, and time.

The trail continues through the beautiful scattered rock formations to Little Rock.

Stay on the trail and make your way up and around the rocks.

The trail climbs up the massive rock formations to the Civilian Conservation Corps Trail junction towards Sentinel Rock.

Enjoy the scenery and landscape!

The carved staircases takes you up and over the natural sandstone structures.

The trail drops down through the mountain brush to the base of Sentinel Rock.

For newcomers, Sentinel Rock at Mount Diablo’s Rock City is a stunner. Sentinel Rock is one of the most popular destinations in the park; yet, for such a prominent feature it is extraordinarily difficult to spot. Once you find it, you will be imprinted forever by the sight of this sandstone monolith and the adventures available there. At its base on the east side, you’ll find something of a carved staircase that starts the trek to the top. Cables are set up to keep you safe.  Kids (of all ages) will have a ball, but be sure everyone stays behind the cable barrier! After the climb, take the opportunity to explore the astounding landscape of Rock City; there are no real trails, but you cannot get too hopelessly lost. Well gripping shoes or boots are essential. *2

Enjoy the panoramic Rock City wilderness views!



Descend Sentinel Rock.

At the base, turn left and head down through the woods for a short scramble along the creek.

The trail comes to a T at Summit Trail, turn left and stay on the trail through upper Dan Cook Canyon towards Live Oak Campground.

Summit Trail opens up to views of a huge sandstone formation and wind caves.

The trail winds down to the Live Oak Campground.

Follow the paved trail around the gorgeous coast live oaks to stay on Summit Trail.

Return through the shaded canyon on Summit Trail to the Green Valley Trail junction.

Go straight along the canyon towards Green Valley.

At the Green Valley trail gate, turn left onto the unmarked Lower Bridge Loop Trail. The single track travels through the scattered oaks and grassland before merging onto Summit Trail.

Go straight and stay on Summit Trail for the return to Mt Diablo South Gate Entrance and Mt Diablo Scenic Blvd.

This is a fabulous hike around the southern part of the park up to Fossil Ridge. Take the time to explore the gorgeous natural sandstone rock formations around Rock City and soak in the phenomenal views at the top of Sentinel Rock! It ROCKS!





8.36 Miles with 1737′ of elevation gain
Max elevation: 1803′
Time: 4.5 hours
Hike: Moderate with steep climbs
Parking: Very limited-max 2 vehicles at south park boundary on Mt. Diablo Scenic Boulevard, a little beyond the Athenian School about 2/10th of a mile south of the South Gate Entrance.
Check map for exact location.
No facilities & no water.
Bring water & food/snacks-Water & restrooms/pit toilets at Rock City & Live Oak Campground

Weather: Sunny & warm. Temps ranging from the mid 60’s to the low 80’s with SW winds

*The current edition “Mount Diablo Trail Map” is available for purchase at the park entrance stations, Summit Visitor Center and Mitchell Canyon Visitor Center in Mt.  Diablo State Park. They are also available at selected retail map distribution stores such as REI, Sportsbasement and on-line at MDIA’s Store.

Direction: Mt Diablo Scenic Blvd > Mt Diablo South Gate Entrance > L-Summit Tr > cross bridge > R-Stay on Summit Tr > R- Stay on Summit Tr > R-W Fossil Ridge Rd > U-W Fossil Ridge Rd > R-Artist Point Tr > L-Exit Artist Point Picnic Are on paved road > R-E Fossil Ridge Rd > U-E Fossil Ridge Rd > to Rock City Live Oak Picnic Area > Follow paved road to Grotto Area-Big Rock, Sentinel Rock & Wind Caves > Explore Big Rock & Elephant Rock > Rock City Tr > Wind Caves & Little Rock > Stay on Rock City Tr-Trail through Time > L-Civilian Conservation Corps Tr > Climb to Sentinel Rock > U-descend Sentinel Rock > L-follow unmarked trail around Sentinel Rock > descend trail along creek towards Summit Tr > L-Summit Tr > Live Oak Campground > R-stay on Summit Tr > S-Green Valley Tr > L-at trail gate to unmarked Lower Bridge Loop Tr > R-Summit Tr > Mt Diablo South Gate Entrance > R-Mt Diablo Scenic Blvd




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