Wide Open Views
Pleasanton Ridge Regional Park is one of the crown jewels in the East Bay Regional Parks District (EBRPD) due to its easy access from the Pleasanton/Livermore/Dublin area and magnificent views. This area is now cattle country, but was once known for fruit production. A prominent trail in the park is the Thermalito Trail named for the Thermal Fruit Company which operated from 1904 until about 1930. Thermal grew non-irrigated cherries, apricots, prunes, and almonds for the dried fruits market. Unfortunately these delicacies are no longer found in the park, but a few decent-sized groves of olive trees still exist. No one is quite sure who planted these olive trees, but it's quite possible that they were part of the Thermal operation.
The hike starts from the Foothill Staging Area which is the park's only access point as far as I can tell though it's quite possible that there are unofficial access points on the north, east, and west sides of the park. Start out going west and uphill on the Woodland Trail. Woodland quickly ascends to near the top of Pleasanton Ridge in just over a mile. The Oak Tree loop trail branches off north .15 mile from the start and also at the end, and it is supposedly quite popular for hikers looking for a short excursion.
The upper end of the Woodland Trail is a 5-way junction. You can head back the way you came, go right onto the upper portion of the Oak Tree Trail, a little further right on the Ridgeline Trail, continue over to the western side of Pleasanton Ridge on the Oak Tree Trail, or to the left on the Ridgeline Trail. The junction isn't a true 5-way junction, but all of these trails meet within about 50 yards of each other. Go right on the Ridgeline Trail. This junction is marked on the official map that's available at the trail head as #5, and is marked on the trail.
The superb views are now quite evident. The Woodland Trail and the flanks of Pleasanton Ridge are heavily forested with a mixture of the various local oak trees, but the top of the ridge is wide open. Mount Diablo to the north, Mission Peak rises to the south, and the slightly-higher Sunol Ridge dominates the view to the west. Pleasanton and Sunol Ridges frame the substantial Sinbad Creek drainage through Kilkare Canyon. These wide open grasslands should prove to be spectacular areas for wildflowers in the spring.
The Ridgeline Trail features a moderate, but noticeable, ascent through a grove of olive trees. Ridgeline Trail continues in much the same fashion, up-and-down, until it reaches marker #16. You can go left (west) here to access the Thermalito Trail, but continuing another .26 mile to marker #18 affords superb views of the Livermore Valley to the east. At marker #18 head left for roughly .10 mile to marker #17 to reach the Thermalito Trail.
Thermalito is similar to Ridgeline in that it travels near the top of Pleasanton Ridge, but Thermalito is slightly lower. Thermalito travels along the western portion of the top of the ridge, and skirts a few stock tanks. The first tank you encounter heading south looks fairly nasty, but the second tank (on the right) looks almost like a natural pond. Indeed it seems to be extensively utilized by native wildlife as evidenced by the numerous deer and turkey tracks. I saw a flock of about a dozen turkeys who were edging towards the water at dusk until I sent them on a cautious retreat.
Just south of this tank you should take the Olive Grove Trail for about 1/2 mile back to the 5-way junction passing markers #13 and then 12. You could continue south on the Thermalito Trail, and return to the junction via the Oak Tree and Ridgeline trails. This adds about another mile. Continue down the Woodland Trail back to the trail head.
This trail is not recommended during warm weather as it's fairly exposed, and temperatures routinely exceed 100 degrees.
Check out the Official Route and Triplog.