On-Site Photographs--Page 2

For Web Site: Early Cambrian Fossils Of Westgard Pass, California

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Directional perspective is southwest along California State Route 168, with eastern side of Sierra Nevada along skyline. Sign along left side of SR 168 informs travelers that they are leaving the Inyo National Forest. Hill and slopes in left half of photograph are composed of shales and quartzites (heat and pressure-altered sandstone) of the lower Cambrian Poleta Formation, deposited approximately 518 to 516 million years ago in a warm, shallow sea then situated near the equator; such predominantly detrital accumulations of the Poleta Formation in the Westgard Pass area typically contain local preservations of Olenellid trilobites, early echinoderms, and annelid and arthropod trails (ichnofossils). Image taken by the Google Earth Street View Car; I cropped and processed it through photoshop.

View is slightly west of due north along California State Route 168 in the White-Inyo Mountains. This is the approach to "the narrows" of the Westgard Pass region. Here sagebrush and pinyon pines protrude from world-famous exposures of archaeocyathid-bearing limestones in the lower Cambrian Poleta Formation, deposited approximately 520 to 518 million years ago in a warm, shallow sea then situated near the equator. Current paleontological consensus is that the archaeocyathid is an extinct variety of calcareous sponge, a member of the phylum Porifera. Image taken by the Google Earth Street View Car; I cropped and processed it through photoshop.

Viewing perspective is slightly north of due west along California State Route 168 in the White-Inyo Mountains. Here, one passes through the classic "narrows" carved in archaeocyathid-bearing limestones of the lower Cambrian Poleta Formation, deposited roughly 520 to 518 million years ago in a warm, shallow sea then situated near the equator. Most recent paleontological analysis demonstrates that the archaeocyathid is an extinct variety of calcareous sponge, a member of the phylum Porifera. Image taken by the Google Earth Street View Car; I cropped and processed it through photoshop.

Viewing direction is northwest along California State Route 168 in the White-Inyo Mountains at Westgard Pass. Exposed here is a classic geologic contact between two world-famous fossiliferous early Cambrian geologic rock units. The roadcut and lower slopes that extend to the ridge in left half of photograph consist of shales belonging to the lower Cambrian Montenegro Member of the Campito Formation, which is locally fossiliferous with spectacular occurrences of Olenellid trilobites some 522 to 520 million years old. The Campito shales here grade upward into the overlying--and, hence younger--archaeocyathid-bearing limestones of the lower Cambrian Poleta Formation, approximately 520 to 518 million years old; the ridge is thus composed of archaeocyathid limestones of the Poleta Formation. Most paleontologist now agree that archaeocyathids represent an extinct type of calcareous sponge, a member of the phylum Porifera. Image taken by the Google Earth Street View Car; I cropped and processed it through photoshop.

Directional perspective is southwest along Payson Canyon, downgrade (north to northeast) from Westgard Pass. Here, State Route 168 cuts through rocks of ever greater primordial age. All slope exposures in view consist of quartzitic sandstones and gray interbedded mudstone and shale of the early Cambrian Andrews Mountain Member (around 526 to 522 million years old) of the Campito Formation, which immediately underlies the Campito's Montenegro Member, seen in the photograph immediately above; and near the top (youngest horizons) of the Andrews Mountain Member, in strata close to 522 million years ancient, the oldest trilobites in North America--and possibly the world--have been discovered, an Olenellid form resembling the Siberian trilobite Repinaella. Image taken by the Google Earth Street View Car; I cropped and processed it through photoshop.

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