–the last posting, (March 21) had a photo of granite of the Cretaceous Sierra Nevada Batholith intruding Cambrian sedimentary (now metamorphosed) rocks. These photos show more Cambrian rock. The Cambrian Period (542-488 million years ago) is the bottom of the Phanerozoic Eon –and one reason Cambrian rocks are significant, is that they are the oldest rocks to contain shelly fossils. Older rocks, called “Precambrian” may contain fossil impressions or fossilized algae, but don’t contain any shells.
At the risk of being too repetitive (see post March 13) the upper photo shows Cambrian limestone in the Death Valley region –there are thousands of feet of Cambrian Limestone in the Death Valley region. The lower photo shows Cambrian sandstone, shale, and limestone overlying tilted Precambrian sedimentary rock in the Grand Canyon.
My point is that the Cambrian section is traceable over great distances. That’s important, because the base of the Cambrian provides a common datum over much of the western US –certainly from the Sierra Nevada to Death Valley to the Grand Canyon –but in later posts, you can see that it’s also in Colorado, Wyoming, Montana… and so on!
The photo above shows the Cambrian Bonanza King Formation (gray) on top the Cambrian Carrara Fm (orange).
And the photo below shows the near-horizontal Cambrian and younger rocks of the Grand Canyon over tilted Precambrian sedimentary rock. It’s really thin here… the Cambrian only goes up through the arrow.