This website was created for the purpose of sharing and disseminating useful information and ongoing research work primarily focused on the Early Tertiary geologic section of the Central Sierra Nevada region of California. That period was an interesting time of geological change for this region. Much more work is required to sort out the influence of the Sierran tectonic and global climate changes that played an important role in determining the character and mineralogy of the rock units emplaced in this province during that time.
Perhaps more than any other geologic unit in the Sierra Nevada, the Early Tertiary sedimentary section has had considerable affect on both historic and modern human activities. For example, the development of hydraulic mining methods that removed incalculable volumes of sediment hosting large concentrations of placer gold (Early Tertiary auriferous gravels) contributed to the rapid economic and cultural development of California beginning in the 1850’s. However, the resulting sediment discharge down the regional rivers inundated vast areas of agricultural lands and led to one of the first major class action environmental lawsuits in the 1880’s.
The more recent economic effect of this section of rock on human activities has unfortunately also been negative. The rapidly expanding urban development in the Sacramento and San Joaquin Valleys and adjacent Sierra Nevada Foothill areas is now encountering and encroaching on the unique form of expansive clay materials in some of these Early Tertiary sedimentary units.
Contributing factors that have led to perplexing geotechnical problems associated with these Sierran sedimentary units include the general lack of knowledge about the character and mineralogy of the clayey constituents in both the Early Tertiary fluvial sediments and the associated regional mature soils from which the sediments were derived during that ancient tropical climatic period; a poor understanding of the mechanism of the transport and preservation of the expansive pedogenic (soil-derived) clayey sedimentary materials in modern and ancient tropical river systems; the inability of the Standard ASTM soil engineering laboratory test methods to correctly characterize the potentially expansive nature of the Early Tertiary soils and sediments; and the deficiency of our modern geologic maps that are largely founded on the archaic late 19th/early 20th Century geologic mapping work. The early mapping efforts failed to differentiate these problematic sedimentary units. These topics are addressed in the documents included in the Geologic Hazards category.
This site is a work in progress and will grow and develop with time. There are numerous interesting geoscience topics relating to better understanding Sierran geology and the paleoenvironment that could/will be included here. In addition to geology and climate, other topics will include Quaternary glaciation, and the legacy of mining in the Sierra Nevada gold country. This latter topic is another that continues to have implications to our environment and ecosystems today.
Check back with us to see what’s new and follow updates for this site on Twitter: @sierrageology.