On the Most Inaccessible Mountain Range on the Planet: Walking the Mid-Ocean Ridge in the Marin Headlands

What is the most inaccessible mountain range on planet Earth? The Himalaya? The southern Andes? Some mountain range in the Antarctic wastes? Nah. The most inaccessible mountain range is so difficult to visit that only a handful of humans have ever even laid eyes on it. It lies at the bottom of the sea, and is called the Mid-ocean ridge. It dwarfs the other major mountain ranges around the planet, extending for around 45,000 miles, enough to nearly circle the planet twice.

The Mid-ocean Ridge is not a high mountain range, maybe 5,000-10,000 feet high, but it lies thousands of feet beneath sea level except in extraordinary places like Iceland. Iceland is part of the Mid-ocean Ridge, but probably also includes magmas rising from a hot spot, giving it the extra elevation to rise above the waves.

So mountaineering on the Mid-ocean Ridge is beyond most mortal folk, but you can explore the surface of the ridge in a few places around the world where oceanic crust has been scraped off the sea-floor and accreted to the edge of a continent. One such place is on the Marin Headlands just north of San Francisco (I noticed in the geoblogosphere that Chuck Bailey at W&M Blogs has recently described another such spot in the somewhat more exotic Wadi Jezzi in Oman - Check it out!).

Some of the most spectacular scenery along the most beautiful coastline in the world can be found on the Marin Headlands (this post is actually a continuation of a blog series I started before the Christmas holidays). When you cross the Golden Gate Bridge headed north, take the Alexander Avenue offramp and follow Conzelman Road onto the headlands. Immediately you are treated with a gorgeous view of the Golden Gate Bridge, but the real story is behind you in the roadcuts. There are ribbon cherts (a form of deep ocean sediment derived from myriads of one-celled creatures called diatoms) lying directly on ocean-floor basalt. Lay your hands on the contact between the two and you are touching the surface of what once was part of the greatest mountain range on planet Earth!

The Marin Headlands don't lack for inaccessibility themselves. The coastline through this region is exceptionally rugged, with steep cliffs that slope directly into the surf. San Francisco Bay lies hidden behind the peninsula, and the ruggedness of the region prevented its discovery for many years (nearby Monterey Bay was visited as early as 1542, but San Francisco Bay was not discovered until 1769).

The odd looking cement structures found around the Marin Headlands are kind of a jarring reminder that the history of this region is not that of long-protected wilderness sanctuary. When World War II was being fought, San Francisco Bay was one of the most important strategic strongholds for the entire Pacific Theater of operations. There was the harbor itself through which much of the fleet operated, factories and ammunition depots, and the inland agricultural areas. That and a huge civilian population. The hills above the Golden Gate were studded with huge cannons and guns that could wreak devastation on any enemy flotilla that tried to enter the harbor. Below is Battery Mendell, just north of the Point Bonita Lighthouse.

The Marin Headlands region is a stunningly beautiful place with a fascinating geological story. The area is protected as part of the Golden Gate National Recreation Area, which is a level of protection that is more or less equivalent to a national park. It is certainly a popular destination, but it's usually possible to find some quiet corners, especially if you are willing to hike a little. While in the area, don't pass up Muir Woods National Monument. It's one of the most-visited monuments in the country, but wandering through the Redwood forest, it's not hard to see why.

Why Did the Military Get Such Nice Digs? Fort Baker on San Francisco Bay

The reasons are partly geological. But before we mention the geology, there must be pictures of cute and interesting animals...like this young sea lion that was eying the crowd of fisherman on the wharf. We were in the Bay Area today celebrating a birthday, but everywhere we went was crowded, as if it were a holiday weekend or something. No parking on the beach at Half Moon Bay. Nothing at either end of the Golden Gate Bridge. The Marin Headlands didn't look particularly crowded from a distance, but the offramp on 101 was backed up for a quarter mile. There was a crowded art festival at Sausalito. We despaired of finding any place to hang out, but a short distance from Sausalito we found a quiet uncrowded park that had somehow missed my notice in the past: Fort Baker.

The military got all the best spots on San Francisco Bay. The Presidio is a huge complex on the northernmost part of the San Francisco peninsula, and the Marin Headlands were covered with forts and outposts, as well as an imposing group of gun batteries. It isn't hard to figure out why. Before the days when wars could be fought with buttons and missiles and drones, you had to assault other countries with some kind of invading force, and if the countries were bounded by shorelines, you had to invade with ships. A brief look at a map of the California coastline reveals that the state has a grand total of two natural harbors: San Francisco Bay, and Coronado Bay down south at San Diego. Two harbors that controlled essentially all major ship traffic south of the Columbia River in Oregon and Washington. Strategically, this is a vulnerability.

The eastern and southern coasts of the United States are geologically stable and are replete with fine harbors as a result of the steep rise in sea level that accompanied the melting of the glaciers at the end of the last Ice Age. River mouths were drowned, providing extensive bays, and deep anchorages.

California is different. It sits on an active plate boundary, the San Andreas transform, and many parts of the coast rise steeply from the depths of the sea. The tectonic uplift has been geologically rapid, and erosion has not kept up in most places. The one exception in central California is San Francisco where the Sacramento/San Joaquin river system was able to carve a canyon through the rapidly rising Coast Ranges. When the ice ages ended, the rise of sea level filled the lower canyon of the Sacramento and San Francisco Bay was the result.

Fort Baker dates from around 1905 when the United States military was beginning to realize the vulnerability of the west coast to attacks by sea. By the time World War II rolled around, the hills above the Golden Gate bristled with cannons. Any armada that tried to enter San Francisco Bay would have been carved to pieces by the crossfire.

The nature of warfare has changed and the gun emplacements and military forts at San Francisco became obsolete. The Presidio was given over to the National Park Service in 1994, and the last soldiers left Fort Baker in 2000. The areas are now managed as part of the Golden Gate National Recreation Area.

On this holiday weekend we discovered Fort Baker was uncrowded and beautiful. There was a simply spectacular view of San Francisco and a unique perspective of the Golden Gate Bridge. There was plenty of animal life to keep us entertained, and from the look of things, the fishing was good. It was a fine day....