Archive for the ‘oakland rocks’ Category

The Skyline median trail

3 August 2015

My latest outing took me to what I’ll call the middle part of Skyline Boulevard, the part where the road is divided. Starting at Skyline High School and going south for about 2 miles, a footpath runs in the median. It’s a hidden gem. This is the nearest thing Oakland has to a long walk on a country lane.


Nobody online talks about this trail. I don’t know who made it or who maintains it. Cyclists laud the paved road, of course, which deserves the praise. The MBTR mountain bikers site reviews it under the name Skyline Boulevard Singletrack and gives it high marks, but you’d have to be as singleminded as me AND a mountain biker to seek it out. But the path is a nice way to enjoy this part of the hills.

This end of Skyline is exclusively on the Oakland Conglomerate, which holds up the spine of the ridge. Here’s the terrain:


And here’s the geology, with “Ko” representing the Oakland Conglomerate (this is the same sequence seen in Shepherd Canyon):


Some parts of the bedrock are straight sandstone.


But almost everywhere along the trail you’ll see the rounded cobbles that are this rock unit’s most distinctive feature, either embedded in stone or weathered out like this.


A slight detour up Brandy Rock Way will bring you to this fine exposure of the vertically tilted bedding, with a thick sandstone bed and conglomerate on either side (1000 pixels).


The road is slightly off the actual crest of the ridge, so the views it offers are mainly over the Bay. Here’s a spot near Cathy Lane overlooking a vineyard, the row homes across Leona Canyon on Campus Drive, the airport tower, the Bay and the San Mateo Peninsula.


I’m thinking that this would make part of a nice ramble. Farther south, Skyline merges into a two-way road and the path continues alongside it. Later this summer I’ll get to that part.

Meet Knowland Park and its rocks

27 July 2015

The neighbors of Knowland Park have something special in their midst: a large stretch of relatively untouched land of the Oakland Hills. If you’ve never been up there, it’s easy to dismiss it. It’s exclusive. You need a car, and there aren’t amy big entrances and signage. Only one bus line (the 46L) goes through it at all, and that’s only once an hour. But I urge you to make the effort some time. There’s nothing else like it anywhere north of Hayward. Here’s a glimpse, looking over the upper part of the park toward the highest hills (click for 1000 pixels).


Some psychologists say that land like this hits a deep, atavistic spot in the brain that’s tuned to our ancestry in Africa. It’s worth testing that hypothesis for yourself.

The Friends of Knowland Park are fiercely protective of this land, but one thing they don’t mention is that much of it is underlain by Franciscan melange, unlike anywhere else on this side of the Hayward fault. We’re looking at it—and see here on the right-hand side: a big old outcrop.


I can’t wait to visit it.

Caballo Hills rocks and views

20 July 2015

The Caballo Hills is the neigborhood flanking Merritt College on the Bay side; it consists of Campus Drive and the Ridgemont development. It’s geologically monotonous, underlain entirely by Leona “rhyolite.” And while all the roads have sidewalks, it’s a steep and exposed hike. Nevertheless the area is highly scenic, and I walked it in the course of a few separate visits this spring.

Let’s start with the map. It shows that essentially all the homes here were built on graded lots, removing whatever soil was there.


I guess the original vegetation was scrub like that on 1175 Hill, the high knob in the Leona Canyon Preserve. Now it’s mostly bare rock. Here’s a typical example, a roadcut on the Merritt College campus.


And here’s another farther down Campus Drive.


So seeing interesting things underfoot is not easy as you visit this area. The “rhyolite” is not a stratified rock—you won’t see bedding, or fossils, or sedimentary features. However, its rusty butterscotch color is very even and pervasive. This is caused by the presence of iron oxides, which are steadily being released from the rock, probably from pyrite and other metal sulfides being oxidized in the presence of air and water.

That’s why this bedrock exposure caught my eye at one spot. It features little pockets of intact pyrite that were exposed by the developers’ excavators.


The Leona Heights sulfur mine exploited this same rock unit, and you’ll see similar pyrite pockets in the rocks exposed there, at the end of McDonell Avenue. Outside the mine area, the rest of the “rhyolite” probably weathers slowly enough that sulfuric acid from the pyrite oxidation is neutralized with no problem.

But lift your eyes off the ground and the best part of this neighborhood reveals itself: the views. I surveyed the Ridgemont end on a cloudy day in April. Here’s a look at the northern end of Ridgemont Drive from the parking lot on the western edge of the college.


And this is looking back up from there. It’s beautiful land. Would be nice if Leona Heights Park could take up some of it.


The south end of Ridgemont overlooks the former Leona Quarry and the uppermost catchment of Chimes Creek.


I surveyed Campus Drive a couple weeks later on a sunny day, which made the hike harder but offered better views. This view is to the southeast (it’s 1000 pixels, click and enjoy). The high ridge in the back appears to be The Knife, an eminence overlooking San Ramon about 8 miles away that reaches over 1800 feet and consists of the Briones Formation.


And this view (also 1000 px) looks right over the old Oak Knoll grounds and Knowland Park hill to the 800-foot peak of Fairmont Ridge.


Down at the southern foot of Campus Drive, you get eye-soothing views of Leona Canyon.


This city is just gorgeous.


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