![alabama hills alabama hills](https://cdn.drivingline.com/media/729211/002_alabama_hills.jpg)
Do you like the temperature outside? “It’s a lovely climate you got here. The fact that the Earth’s climate can shift between warmer and colder states is a fundamental insight of modern climate science. Clambering around in that transition zone, you’d doubtless find faceted erratics and striated bedrock. The name “Sierra” reflects this – it is Spanish for “saw.” The cornucopia-like shape of the valleys we can see speaks plainly about the changing stability field of ice as elevation decreases. This glacial erosion hewed the mountain range into a new shape, a sequence of peaks separated by valleys, like the teeth on a saw. During the Pleistocene epoch, the “Ice Age,” the Sierras were swathed in glaciers, with ice flowing downhill under its own weight, plucking and abrading and gouging thereby into the tough rock from which the mountain was made. Some of the valleys draining to the east have a wide, U-shaped profile at their tops, and transition to narrower, V-shaped profiles downslope. The high Sierra has been glaciated, and even retains some permanent icefields and “glaciers” to this day. There’s almost 10,000 feet of vertical difference between Mount Whitney’s granite and that of the Alabama Hills. They are subjected to radically different weathering conditions than the Alabama Hills (at only ~5300 feet of elevation). Up high on the Sierra crest, peaks like Mount Whitney (the chunky peak at left, adjacent to the two spiky Keeler Needles) poke up to more than 14,000 feet above sea level. They are the roots, the plumbing, of a continental volcanic arc akin to that operating in the modern day in the Andes.īut in spite of their common lithologic identity, the granites on either side of the fault look strikingly different.
![alabama hills alabama hills](https://californiathroughmylens.com/wp-content/uploads/2012/09/Alabama-Hills-Ambush-Point.jpg)
The rocks on both sides of the fault are Cretaceous granites -the crystallized results of multiple silica-rich magmatic intrusions into the edge of the North American crust during a protracted period of subduction during the Mesozoic. The local example is the Sierra Nevada Frontal Fault, the one we gaze across in this image. At the surface, this deformation is taken up along normal faults, with the hanging wall dropping down to make Basins, and the footwall left high and dry as a Range. This oblique shear (transtension) has caused the rocks between the eastern Sierra and the Wasatch Front to have been stretched most profoundly from east to west.
![alabama hills alabama hills](https://live.staticflickr.com/1600/24421763276_eedcaf11a3_b.jpg)
For the past 30 million years, the west has been widened, the tectonic stresses imposed by the plate boundary to the west being taken up not only by the San Andreas Fault, but also to a lesser degree (~15%) by deformation a good distance into the continent. The many north-south-trending faults of the Basin and Range are due to the singular tectonics of the western United States. The two are separated by the Sierra Nevada Frontal Fault, which is the first of the Basin and Range normal faults headed east from the Pacific Coast, and the dividing line between the Sierra Nevada and the Basin and Range. Next up, let’s look at the more Earthy subjects: the mountains and the foreground. Though it’s far, far away, the moon is sufficiently lit that we can distinguish between its older anorthositic highlands and its lower, younger basaltic “maria” (lava flows filling impact craters). It appears to be late morning or mid-day, on the basis of east-facing slopes being well lit and not in shadow. This is in the northern hemisphere we’re looking westward. The sun is off to the left, to the south. We note that the orientation of the shadow of the moon is identical to the shadows we see on the rock outcrops in the foreground. The blue of our atmosphere surrounds that lovely orb, approximately 2/3 lit. But we are not alone: looking up into the space adjacent to our planet, we can make out a moon. Let’s start with the biggest picture: this photo shows a portion of our planet, Earth. This image shows the Alabama Hills outside of Lone Pine, California, in the Owens Valley, looking west at the eastern slopes of the Sierra Nevada mountain range.
![alabama hills alabama hills](https://californiathroughmylens.com/wp-content/uploads/2012/09/Alabama-Hills-15.jpg)
Gaze upon its majesty, ye mortals, and rejoice:Ĭlick through to enlarge. My friend Barbara am Ende posted this image on Facebook the other day, and I instantly swooned over its myriad teeming geoscience lessons.