Friday Rocks 6: Sierra Nevada Roof Pendant

Photo by Tim Sherry

A roof pendant is a unit of country rock that sits on top of an intrusive igneous body. Here the dark rock at the top of the ridge was baked in a process called contact metamorphism by the Sierra Nevada igneous batholith. I couldn’t find an exact name of this particular roof pendant. If you can name it, let us know in the comments!

Friday Rocks 5: Baby Duplex

photo by Tim Sherry

Here we have a thin sandy-mudstone bed (~20 cm thick, sorry for no scale) at MontaƱa de Oro State Park, California. The two diagonal leaning fractures are small thrust faults that bound a block of the original bed creating what geologists call a “horse”. On the left side of the photo a small backthrust is present. The faults are not continuous across the siltstone beds above and below this layer. The sedimentary bedding in this area is typically planar, but some flexure is present as seen in the photo below.

photo by Tim Sherry

Here the siltstone is deformed by the sandy-mudstone load casts (thanks Greg!).

Friday Rocks 4: Stylolites in Limestone

Photo by Tim Sherry

The thin red-brown wavy band in this limestone is a stylolite. Stylolites are formed via a process called pressure solution and is the result of a volume decrease in the rock during diagenesis. Material, usually in the presence of a fluid, is dissolved and transported away, leaving a wavy band of material. Here the stylolite is roughly parallel to horizontal laminae in the limestone. Photo taken in the Poleta Fold Belt, Eastern California.

What’s your graphic CV?

Graphic Designer, Artist, and Geologist Carissa L. Carter has an unusual CV on her website. A graphical CV with interests on the y-axis and time on the x-axis.

Carissa’s Graphical CV

I like this way of presenting how ideas and interests change over time. Maybe focusing even closer on a specific topic, like geology, to explore changing interests in subtopics. Someone with many publications could even generate a graphic like the one above simply from publication topics. How has what you think about changed over the years?

Check out the Carissa’s graphic CV here: http://goo.gl/AieNGf

Also, wanted to highlight a little Geology-As-Art from Carissa’s site. The shoe stratigraphic column. Explore it here: http://goo.gl/ShsWnt

Her website is http://www.snowflyzone.com/

Friday Rocks 3: Rhyolite Rosets

 The Bishop Tuff is a welded ashflow that was deposited ~700,000 years ago (Dalrymple et al, 1965). Here the Owen’s River incised the Bishop Tuff exposing beautiful columnar rhyolite. The columnar fracture pattern is made by rapid cooling caused be a fumeral of escaping steam. Water that the Bishop Tuff was deposited over was heated and pressurized, leading to an explosive escape through fumarole mounds that dot the region. The roset, curved jointing is orthogonal to isotherms and tubes of escaping hot water (Sheridan, 1970).

All photos by Timothy Sherry

Dalrymple, G. Brent, Allan Cox, and Richard R. Doell. “Potassium-argon age and paleomagnetism of the Bishop Tuff, California.” Geological Society of America Bulletin 76.6 (1965): 665-674.


Sheridan, Michael F. “Fuarmolic Mounds and Ridges of the Bishop Tuff, California.” Geological Society of America Bulletin 81.3 (1970): 851-868.