The type locality for the Hanson Creek Formation is the north fork of Pete Hanson Creek on the northwest flank of the Roberts Mountains, 35 miles northwest of Eureka (Merriam, 1960).

The Ordovician/Silurian boundary lies within the upper 20-40 meters of the Hanson Creek Formation (Mullens and Poole, 1972). This upper portion is considered lower Llandoverian in age, while everything beneath bears an Ashgillian age. In the Monitor Range, the Hanson Creek is Late Ordovician (Caradocian to Ashgillian) in age (Kleinhampl and Ziony, 1985).

The Hanson Creek is a time equivalent of the Ely Springs Dolomite to the east and south, as well as the Fish Haven Dolomite to the northeast, and the Copenhagen Formation in the Monitor-Antelope Range area. The complication of nomenclature is unfortunate since all three units are actually one relatively consistent time-stratigraphic sequence, and the name applied to the dolomite has been somewhat arbitrary. A dropping of Fish Haven within Nevada, and retainment of either the Hanson Creek or Ely Springs Dolomite designation would greatly simplify an unnecessarily complicated terminology.

In general however, the name Hanson Creek is retained in western sections from the Cortez Mountains (Gilluly and Masursky, 1965) to the Diamond Mountains (Nolan and others, 1974). The Ely Springs Dolomite is retained in central sections from the Pancake Range (Quinlivan and others, 1974) on the west through Lincoln and White Pine Counties (Tschanz and Pampeyan, 1970) to the Cherry Creek Range. The Fish Haven is used for sections along the eastern edge of Nevada and into western Utah. This includes the Pequop Mountains anb Red Hills, Goshute, Snake, Egan, Schell Creek, Deep Creek, Silver Island, and Pilot Ranges (Whitebread, 1969; Nolan, 1935; Blue, 1960; O'Neill, 1968; Kellogg, 1963; Drewes, 1967; Thorman, 1970).

Various thicknesses and types of mudstone, algal boundstone, wackestone, packstone and grainstones are present in the Hanson Creek Formation at different localities. The single common characteristic of Hanson Creek sections is a shoaling upward sequence often seen as a transition from deep water carbonate mud upwards into quartz-oolite sands and skeletal carbonate (Dunham, 1977). A thin sand is often present near the base of the formation.

At its type section within the Roberts Mountains, the section is composed of gray dolomite and silty limestone, and becomes entirely dolomite near Eureka, Nevada (Ross and others, 1979). The Hanson Creek shows a basal (85 feet) dark-gray to black, medium-grained, dolomitic limestone which grades upward into finely laminated, medium to dark-grey limestone with black chert nodules. The middle unit (280 feet) is fossiliferous, thinly and poorly bedded, shaly, dark blue-grey limestone. The upper unit (180 feet) is fine-grained, massive limestone and contains an uppermost 15 foot thick bed of chert (Roberts and others, 1967).

In the Eureka district and Tuscarora Mountains, the Hanson Creek is a dark-grey to black, massive, coarse-grained dolomite with thinner-bedded interstratified grey and black dolomite towards the top (Roberts and others, 1967). To the east at Schroeder Mountain, the upper 150 feet of the Hanson Creek are exposed and are composed of medium-gray and black, highly fractured, massive dolomite with irregular blue-black chert lenses and beds up to 2 inches thick and 2 feet long (Cress, 1972).

In the Cortez Mountains, the Hanson Creek is composed of three members with an aggregate thickness of 480 feet (Gilluly and Gates, 1965; Gilluly and Masursky, 1965; Roberts and others, 1967). The lower member is a black, steel-gray weathering dolomite with "elephant hide" texture. The middle member is thick, light gray-brown, siliceous limestone. The upper portion of the formation is light gray, massive dolomite, with an upper 5-15 foot thick bed of black, massive fossiliferous dolomite. Near Cortez, the Hanson Creek conformably overlies the Eureka Quartzite and conformably underlies the Roberts Mountains Formation (Stewart and McKee, 1977).

In the Shoshone Range at Goat and Horse Mountain windows, the Hanson Creek is a light to dark gray, banded, coarse-grained dolomite, and bluish-gray, platy, very fine-grained limestone that weathers pale orange (Gilluly and Masursky, 1965; Gilluly and Gates, 1965). The limestones in the Shoshone Range are highly fossiliferous, containing abundant brachiopods, graptolites, and trilobites. Contact relationships and thickness are obscured by faulting (Stewart and McKee, 1977). Faults mark either or both the top and bottom of the Hanson Creek Formation in the Shoshone Range (Gilluly and Gates, 1965). The lower contact, where unfaulted, appears to be conformable and perhaps gradational through a few inches of sandy dolomite with the underlying Eureka Quartzite. The formation is overlain conformably by the Roberts Mountains Formation in the Goat window.

In the Toquima Range, the Hanson Creek Formation is exposed within the Petes Canyon window where it is up to 75 feet in thickness. The lower portion of the formation here is massive, dark, cherty limestone overlain by thinner bedded cherty limestone, and dark-red to green shale in the middle of the unit, and thin-bedded limestone, cherty limestone and lenticular chert beds in the upper part of the unit (McKee, 1976). The Hanson Creek grades upward into the basal black chert of the Roberts Mountains Formation in the Petes Canyon area.

In the Monitor Range near Clear Creek and at Minature Grand Canyon, the formation is a light to dark gray silty dolomite in the lower portion, with an overlying thinner-bedded, tan to brown and pinkish weathering, silty and argillaceous dolomite above (Wise, 1977; Kleinhampl and Ziony, 1985). At Copenhagen Canyon in the Monitor Range, the Hanson Creek is composed of three units (Bortz, 1959). The basal 372 feet are thin-bedded, dark-gray to brown, calcareous shale, and alternating medium-gray, argillaceous limestone with rare chert laminae. This is overlain by about 85 feet of aphanitic, cliff-forming, dark-gray limestone with dark-gray chert beds and lenses. The uppermost unit is about 36 feet of finely crystalline, thin-bedded to massive, light to medium-gray limestone, with silty interbeds and abundant crinoid stems (Bortz, 1959).

In the Hot Creek Range, the Hanson Creek is massive, light-gray to pinkish weathering, flaggy dolomite and dolomitic limestone which grades upward into the overlying Roberts Mountains Formation (Quinlivan and Rogers, 1970; Kleinhampl and Ziony, 1985).

In the Pinon Range, the Hanson Creek is thin to thick-bedded, fine-grained, dark gray to black dolomite with a few interbedded limestones and locally abundant corals and brachiopods (Smith and Ketner, 1975). Locally, light gray and black bands of dolomite alternate in beds up to 4 inches thick, and patches of pink weathering, coarsely crystalline dolomite are present in the unit. The top of the formation is about 20 feet of silty limestone, calcareous siltstone, and very fine-grained yellowish weathering sandstone (Smith and Ketner, 1975).

In the Independence Mountains near Seetoya Peak, the Hanson Creek is present in several fault slices, and appears to conformably underlie the Roberts Mountains Formation (Coats, 1985). In the thickest of these slices, the Hanson Creek is about 340 feet of bedded gray calcisiltite with beds and nodules of black chert, overlain by about 40 feet of gray silty dolomite, and 365 feet of dark gray calcisiltite in beds 1 to 2 inches thick (Kerr, 1962).

In the Snake Mountains, the Hanson Creek is gradationally overlain by the Roberts Mountains Formation. The unit generally consists of a basal, massive and fossiliferous, dark-gray, fine to medium-grained dolomite which is sandy near the base, and interbedded light gray, coarsely crystalline limestone and interbedded gray dolomite (Gardner, 1968; Peterson, 1968).

The thickness of stratigraphic sections varies considerably between, as well as within ranges, based upon the position of the section along the Upper Ordovician- Lower Silurian carbonate platform. The Hanson Creek varies from 75 (Toquima Range) to 600 feet (Shoshone Range) in thickness, and commonly is about 300 feet thick. Sections are often tectonically disturbed since they represent thinly and moderately thickly bedded limestones and dolomites sandwiched between two resistant and massive sequences (Ross and others, 1979).

The Hanson Creek Formation is 190 to 270 feet thick at Clear Creek in the Monitor Range (Wise, 1977; Greene, 1953) and 496 feet at Copenhagen Canyon in the northern Monitor Range (Bortz, 1959), 75 feet thick in the Rawhide Mountain area of the Hot Creek Range (Ross, 1964), 130 feet thick in the Carlin-Pinon Range (Smith and Ketner, 1975), 535 and 724 feet thick in faulted sections in the Independence Mountains (Kerr, 1962; Coats, 1985). 150 feet of the upper portion are preserved at Schroeder Mountain to the east of the Tuscarora Mountains (Cress, 1972), and 1,000 to 1,075 feet in the Snake Mountains (Peterson, 1968; Gardner, 1968).

The Hanson Creek is found on Lone and Schroeder Mountain, and within the Toquima and Shoshone Ranges, Tuscarora, Roberts, Simpson Park, Diamond, and Cortez Mountains, Sulphur Spring, Monitor, Hot Creek, Antelope and Pinon Ranges, Independence and Snake Mountains.

The carbonates of the Hanson Creek Formation were deposited in four distinct environments. These include high energy shoals, open marine waters, low energy subtidal shelf lagoons, and along peritidal mudflats (Dunham, 1977). Moderately sorted quartz carbonate grainstones indicative of high energy shoals, overlie well sorted high energy strand or shallow shoal-type sands of the Eureka Quartzite at Lone Mountain and in the Roberts Mountains. Lagoonal muds of the Hanson Creek overlie the Eureka at Martin Ridge in the northern Monitor Range, Arctic Canyon in the Cortez Range, Coal Canyon in the Simpson Park Mountains and within the Sulphur Spring Range (Dunham, 1977; Gilluly and Gates, 1965). This suggests a northwest-southeast-trending transition from open marine to lagoonal environments (Dunham, 1977).

The generalized paleogeography of the unit is an Upper Ordovician platform receiving shallow subtidal lagoonal sediments north of Lone Mountain and shallow open marine sedimentation to the south. A small basin may have been present along the shelf margin in the present area of the southern Monitor and southwestern Antelope Ranges. This basin had a maximum depth of perhaps 100 meters and received slow accumulation of lime mud and clay to maximum depths of perhaps 100 meters. The upper Hanson Creek is composed of tidal flat and lagoonal deposits throughout Eureka County, which represent a shallowing environment throughout the Lower Silurian.

In general, the dark dolomites of the Ely Springs and Fish Haven represent restricted shallow shelf deposition while the Hanson Creek Formation was deposited in deep or better circulated waters (Ross, 1977). This is indicated by the dominance of limestones over dolomites in the Hanson Creek Formation. The abundant corals and brachiopods in Hanson Creek dolomites indicate replacement of limestones formed under well-circulated conditions. The Ely Springs and Fish Haven Dolomites were formed where water was restricted in lagoons, or over shallow shelves many hundreds of kilometers in width.

A sharp knife edge contact exists between the Hanson Creek and underlying Eureka Quartzite, and has been interpreted as a scoured erosional contact in several localities (Dunham, 1977), and as tectonic contact in the Fish Creek Range and Mahogany Hills (Ross and others, 1979). Thinner bedded units within the Hanson Creek are often intensely folded.

The Hanson Creek often has a strong petroliferous odor on fresh break. In outcrop the formation has some intercrystalline porosity and shows potential for fracture enhancement of permeability. Its structural position between two competent and resistant units makes it an excellent layer in which strain can be accommodated. This results in fracturing and faulting, and folding on various scales within the Hanson Creek Formation.