In the HD Range in northeastern Elko County, the Noh Formation was described by Riva (1970) and consists of a basal, dark-gray chert and light-gray shale, light-brown weathering, siliceous and tuffaceous siltstone and shale, and tan- and light-brown-weathering, thin-bedded siltstone, sandstone, and minor shale. It contains a large and diagnostic Wenlockian (Early Silurian) graptolite fauna, and is partly coeval with the base of the Roberts Mountains Formation (DSt) which also has a conspicuous basal chert ledge. The similar age Elder Sandstone in Lander and Eureka Counties was named for moderately cemented sandstones exposed in the Shoshone Range (Gilluly and Gates, 1965). It is primarily a fine-grained, silty sandstone, sandy siliceous and tuffaceous shale, and thin, platy, light brown chert. Much of the sandstone and siltstone is notably feldspathic, including abundant angular fragments of potassium feldspar, and has reportedly interbedded rhyolite in places (Theodore, T., oral commun., 2006). It is grouped with unit DCs or DOts in many places. Its unusual lithologic characteristics warrant a separate grouping where it can be separated from these units (Noble, Finney, and Cluer, 2000). Zircon studies have suggested that the feldspathic source material for these rocks was not located adjacent to the Nevada part of the continental margin, but is derived from a source either farther to the north or in Mexico (Gehrels, Dickinson, and others, 2000). Likewise, tuffaceous source material for the shale described in the Noh Formation is not known from the Nevada continental margin of this time. Like most other rocks of the Slope and Basin assemblages, unit Ss is everywhere in structural contact with other Paleozoic rocks. It is structurally imbricated with units DCs, DOts, and MDst. Whether these rocks have traveled a significant distance either toward or along the margin as discrete tectonic blocks or as sediment transported in offshore turbidity systems is not known, but no basement is preserved with them, and they are unconformably overlain by the Pennsylvanian and younger Siliciclastic overlap assemblage.