Cabrillo Peak

I was wondering what kind of rock the peaks around here are...The guide says "granitic" but it is more like sandstone to me. I describe it as a cross between sandstone and granite. Anybody know for sure?

OK Jody, I'm going to do my best to respond to your Dacite question. Real geologists will probably have to correct me, but here goes. All of the Morros have a similar chemical composition composed of a type of basalt called "Dacite". Dacite is an igneous rock, meaning it formed deep within the earth. Unlike volcanic rocks (such as the dacite found at Mt. St. Helens), our dacite cooled underground rather than being spewed forth in a volcano. They call that an "intrusive rock" (meaning cooled underground) rather than "extrusive" (meaning cooled above ground such as the lava in Hawaii).Dacite is generally characterized by a high concentration of silica (same stuff glass or sand is made from). It's like granite in that granite also cooled underground (instrusive). The slower cooling results in larger crystals within the rock. This results in better friction and really solid rock for climbing. It's also like granite in that it has a very similar blend of chemicals or minerals inside it (such as silica, which makes up quartz, and feldspar).

OK, now Sandstone. It's nowhere close to sandstone. Sandstone is a sedimentary rock, meaning it's made of layers of (guess what) sand that have been squeezed & smashed together over time to form rock. Our local sandstone is typically made from old seabeds that have been compressed underground and then tilted or lifted to be exposed for us rock climbers. You can see this best on your way to Santa Barbara. Sandstone is not "cooked" underground like dacite or granite so it's nowhere near as hard. The only similarity is that the sand in sandstone is made up primarily of quartz crystals (silicon dioxide) that are ground up into little bits and then squished together.

To summarize, dacite & granite are formed deep underground & cooled slowly and sandstone is formed by squeezing together layers of sand until you get rock. All of this basically takes a really long time. By happy accident, we get to live in an area with both good sandstone & good dacite that is great for climbing.

Basically, the only thing you need to remember is that if you call our local morro rock sandstone, you risk being called a dork! :o)

Thanks John. I knew it wasn't sandstone...it is just that it has more of the texture of bullet sandstone than granite so I thought "granitic" was the wrong way to describe it. My guess(since my last geology class was in college in 1983) was that it was some sort of igneous volcanic plug. Don't worry, I don't call it sandstone...don't want to risk being called a "dork".LOL! Thanks for the info.

Hiked up to Froggy Hill(I think that is what it is called) on the north side of Cabrillo to boulder. Well, at least I started to hike up there. Didn't get ten feet up the trail before I swiped ten ticks off my pant legs. Hadn't even brushed up against any grass. Forget that! I would rather of stepped on a nest of rattlers. I hate ticks! No climbing anything in the area until winter now. Any of the other Cerro's have them this bad?

That place is loaded with ticks. It's Tick City baby! I've been there every season & always get ticks. Try hiking in to the Burial Grounds. There's a 10 tick minimum just to get there. Wear long, light colored pants & you'll be fine!

john

Didn't encounter an owl last weekend but I found a decapitated rat on a ledge below the three bolt ancor at park ridge rocks. I'm a new climber and it was my first time to the area. There were a lot of bolts for the size and difficulty of the rock, it was much appreciated though. It made TR set ups very easy.

More at http://en.wikipedia.org/wiki/Cabrillo_Peak