Saturday, June 21, 2014

La Costa Avenue Garden Migmatite

Migmatites and other high-grade metamorphic rocks are popular garden stones because of their dramatic features and textures.  Today we have a couple of pictures from the front yard of someone's home along La Costa Avenue in Leucadia, California.
We have a nice migmatite in the center of the image with well defined folds.  The surrounding stones are granodiorite most likely quarried from a location in the Southern California Batholith.
Another migmatite from the same front yard with a different texture than the above picture.

Friday, June 20, 2014

Karl Strauss Brewery Migmatite and Gneiss

The stereotypical image of a geologist often brings a few things to mind, but one of the most commonly perceived notions is that geologists like to drink, especially beer.  When you stumble upon a location that combines geologists love of alcohol and rocks together you get their equivalent of Disneyland.  At the Karl Strauss Brewing Company located in Sorrento Valley, California you have the chance to wander around and view a beautiful array of migmatite and gneiss boulders (high-grade metamoprhic rocks) that display all sorts of features before and after you have a pint of beer.

High-grade metamorphic rock with unique features including faults on the left and right side of the block, unique vein like red garnet crystal arrangement, a Z-fold in the middle, and a boudin just to the right of the Z-fold.
This boulder appears to be foliated with some sense of shearing happening.  Although it's hard to interpret, it's possible we can see ptygmatic folds which are common in migmatites.
This boulder is a little more weathered in appearance compared to the other ones in the parking lot, but still displays some great features.  These include a large assortment of faults, dikes and dikelets, and garnets which can be seen on the bottom-right of the boulder as brown dots.
Another migmatite boulder with some beautiful foliation.
Finally we get to this giant boulder that displays many of the features that I have pointed out in the pictures above it, see if you can find some of the features for yourself!

Thursday, June 19, 2014

Santa Monica Migmatite Garden

The city of Santa Monica in western Los Angeles, California is a colorful community that mixes many cultures and a wide variety of home architecture.  In the front yard of a home just west of I-405, north of I-10, and west of Sawtelle Boulevard, a garden boasts an incredible display of migmatites.  Migmatites are often formed through partial melting deep beneath mountain ranges.   I do not know where these migmatites came from, but if any reader knows of a potential quarry where these were taken, please let me know.
Migmatite with a distinct contact between metamorphosed igneous rock with sinistral kinematic indicators sandwiched between gneiss on the top and bottom.
A clearer image of the contact between the meta-igneous and metamorphic rock in this migmatite.  Note the well developed red garnet crystals in the top right of the gneiss.  The gneiss also appears to be slightly foliated.
A little closer look at the contact between meta-igneous melt and gneiss.  Notice how the contact isn't as seamless here with parts of the melt slightly fingering into the gneiss possibly as a result from the partial melting.

Urban Geology: Every Day Rocks

Welcome to Urban Geology, a blog dedicated to discovering and documenting the use of rocks and other geologic phenomenon in urban settings.  Many geologists seek out the wonders of our natural world in remote locations, but many times you can find the great beauty of geology in your own neighborhood.  Whether your city has plutonic rocks used as building stone, charnockite sidewalks, folded strata in the canyon behind your house, or if you have beautiful looking rocks in your garden, this blog will document people's discoveries where they live to show the rest of the world.  Please feel free to contact me if you have a story to share and be sure to include the city, location, rock type(s), pictures, history, and any other description that would generate a good post.  The best way to get your submissions posted is to e-mail me at and write a description of the rocks you have found, their location, clear pictures with a scale to get a reference on the size, and any captions you wish to include.