Point Año Nuevo from the air, with Año Nuevo Island to its left. When Sebastian Vizcaino sighted this point on New Year's Day 1603, the island was part of the mainland.

Point Año Nuevo gets a crush of visitors during the mating season of elephant seals, a spectacle well worth the trip down the San Mateo coast. The rest of the year, especially at low tide, is good for enjoying the Point's geology. For instance, nowhere else on the California coast is a major fault zone so well exposed.

But first let's notice something about the Point: it's all a big flat space. In fact, looking at it from the edge, down on the beach, you'll see that it's a classic marine terrace, just like ones I've described previously at Pebble Beach a few miles to the north and at Shell Beach in Sonoma County.

Photos by Andrew Alden

The top layer of this geologic cake is a thin frosting of brown soil, some orangish stream deposits just beneath it and lighter-colored beach sands. The bottom layer is solid rock all the way down to the beach. The contact between the two layers is a strip of vegetation, where groundwater collects. That contact represents an ancient wave-cut platform, from a time about 105,000 years ago (105 ka) when the sea level was higher than today (because the glaciers had melted even more than they have today).

Here's a closer look at that wave-cut surface. It appears just like the modern seafloor, complete with the borings of pholad clams.

The reason I could photograph this without having to climb the cliffs is that the ground in places has been faulted since 105 ka.

Field trip leader Gerald Weber of UC Santa Cruz lectures at a downdropped wave-cut terrace. Behind him, this surface is several meters higher.

Time to look at the geologic map, which shows several faults crossing Point Año Nuevo. The photo above is from the beach cliff above the word "Bay."

Extracted from USGS Geologic Map of San Mateo County (http://pubs.usgs.gov/of/1998/of98-137). Click image to see a larger version. Qmt, marine terrace; Qs, dune sand; Tsc, Santa Cruz Mudstone; Tp, Purisima Formation; Qyf, active alluvial fan; gold color, older alluvial fan deposits. Año Nuevo Island is Monterey Formation.

All of these faults are part of the San Gregorio fault zone, an obscure part of the San Andreas family that runs mostly offshore. It is thought capable of a very large magnitude 7.5 earthquake. The two most prominent strands at Point Año Nuevo are on the right-hand side of the map; they're informally named the Coastways fault (on the east) and the Frijoles fault. The Frijoles is at the center of this view:

This closeup shows where Año Nuevo Creek, long ago, took advantage of the downdrop on the fault and cut into the underlying Purisima Formation (which is about 5 million years old).

Point Año Nuevo is a very active place today, even though no large earthquakes have been documented here for about a thousand years. When first logged by European explorers in 1603, there was no island here. By the end of the 1700s there was one. Researcher Gerald Weber, who has tramped the Point since 1973, has evidence that this change created a huge washout of sand that protected the southern seacliffs of the Point until just recently. In a field trip recently, he paced off the amount he has seen the cliffs retreat since about 1980. The hat sits where renewed erosion uncovered an old pier post dating from the 1850s, when the pier served lumbering operations in the nearby hills.

Weber thinks that this sand has moved down the coast and is now affecting Santa Cruz Harbor. Eventually it will spill into Monterey Canyon and wash out to the deep sea.

The San Gregorio fault zone is an important mystery. This image from an old map shows its extent in this part of the San Mateo coast.

Recent mapping has improved this picture, but the work is very difficult. Lidar technology promises big advances, though. This light-based form of radar mapping allows us to strip buildings and vegetation off the underlying ground surface, making even subtle fault features stand out. Lidar imagery now covers this region:

Courtesy www.opentopography.org

. . . and the Frijoles fault trace on Point Año Nuevo stands out beautifully in it.

Learn more about Point Año Nuevo's geology from the park's 2009 docent training materials.

Lidar data from many Northern California fault traces is freely viewable in Google Earth.

A Northern Elephant Seal at Ano Nuevo State Park.

We headed west, then south down the coast to the site of the largest mainland breeding colony of the massive Northern Elephant Seal: Ano Nuevo State Reserve.

The Northern Elephant Seal is named for the large, protruding nose, or proboscis on the male of the species. Like elephants, they are also gigantic. The bulls can grow up to 16 feet long and weigh up to 5000 lbs, while the females are much smaller.

On a hike guided by a knowledgeable naturalist volunteer, Scott, our staff spent 1.5 hours traipsing over the dunes to see the winter breeding action of this charismatic pinniped. Getting respectfully close, we first saw what they referred to as "Loser Males". Though this term felt a bit un-PC (how about "mating-challenged?"), the idea is that these males are not old enough or savvy enough to be an alpha or beta male. They are simply not in the competition this year, so they lounge away from the females, thermo-regulating by flipping sand on themselves and holding fins up into the ocean breeze.

We then came upon a pile of weaners. This is another fine term used to describe the young pups that are newly weaned from Mom. These co-ed pods spend time losing some of their 300 lbs of milk fat while they learn to swim in the rain water pools. Born at 70 lbs, pups are nursed for a month or so before they gain weight and take on their new role as weaners. Some pups nurse from two or three females and gain up to 600 lbs. These are then dubbed Super Weaners. The weaners are the last to leave the site, waiting until the adults have gone to take their time swimming away in the salty waves.

Towards the shore the real show was on; Females (cows) gathered in harams, some nursing pups. Males (bulls) fought other males, or at least postured, in order to establish dominance and control of the harams. In one case, a masculine fellow came after another male, blubbering up towards him with full barks, only to then claim his seawater puddle. The fights between males are usually short, but very dramatic and violent. According to Scott, an Alpha Male Elephant Seal in mating-mode has more testosterone than any other mammal.

Our staff left feeling like weaners ourselves; happy and exhausted, but not as exhausted as Scott, whom I am sure has never fielded as many questions as he did for our staff!

Breeding Season at Ano Nuevo is December 15-March 31. In spring and summer, the elephant seals return to molt.

The Ano Nuevo Interpretive Program is excellent and popular. Book a guided tour and check out the dominance displays!

After your tour, visit the gift shop at the site. On your way home, I recommend the town of Pescadero for artichoke bread at Arc Angel Grocery Company & Bakery or the San Gregorio General Store.

Amy Gotliffe is Conservation Manager at The Oakland Zoo.

latitude: 37.1266, longitude: -122.3344