Wellsville Mountain is 10 miles west of Logan, Utah, at the northern extremity of the Wasatch Range. Paleozoic rocks forma northeast-dipping homocline bounded in part by northwest-trending high-angle faults and cut by a series of northeast-trending high-angle faults. A major transverse fault, with a stratigraphic displacement of 4,500 feet, divides the mountain into two distinct blocks. The rock units of the area are comparable to those of the Logan quadrangle immediately to the east. Pre-Cambrian rocks crop out in Box Elder Canyon, just east of Brigham City, and are overlain by at least 20,000 feet of northeast-dipping Paleozoic rocks of every period except possibly the Permian. The Beirdneau sandstone member of the Jefferson formation, is tentatively correlated with that of the upper Devils Gate limestone of central Nevada. About 6,600 feet of the Oquirrh formation of Pennsylvanian age is exposed near the northern end of Wellsville Mountain. The presence of Desmoinesian fusulinids at the base of the Oquirrh and upper Virgilian fusulinids throughout the interval from 1,000 to 2,000 feet above its base indicates an absence of Lower Pennsylvanian rocks and suggests that the upper 4,400 feet may be in part Permian. Mesozoic rocks are not found in the area. The Wasatch formation and Salt Lake group of Tertiary age crop out in the foothills at the northern end of Wellsville Mountain. Two fault systems are recognized in the area. The northeast-trending high-angle transverse faults of Laramide age and the north-west-trending high-angle bordering faults are Basin and Range age.

Wellsville Mountain forms the extreme northern end of the Wasatch Range in northern Utah. It lies at the western margin of the Middle Rocky Mountain province and is bordered by valleys of the Basin and Range province. Many geologic investigations have been made in this region. Much of the Wasatch Range has been studied and mapped as well as parts of the Bear River Range, east of Cache Valley, and the Malad Range which extends north from Wellsville Mountain; however, the geology of Wellsville Mountain has not been studied or mapped in detail. Some reconnaissance mapping has been done and sections of Cambrian and Pennsylvanian formations have been measured on the western mountain front (Maxey, 1941; Williams, 1943), but little is known about the middle Paleozoic formations and the structural geology of the northern part of the mountain.

The Nounan Formation in north-central Utah thickens northward from 696 feet near Causey Dam to 1147 feet at High Creek in the Bear River Range, and northwestward to 1149 feet at Dry Canyon in Wellsville Mountain. The basal contact of the Nounan Formation is sharp, but dolomite extends irregularly downward into limestones of the Bloomington Formation as much as 6 feet. The Nounan Formation is divided into three members based on lithologic characters: (1) a lower member composed of dark, medium-crystalline dolomite; (2) a middle member composed of white, coarse-crystalline dolomite with tongues of dark dolomite; and (3) an upper member of interbedded light and dark dolomites and limestones with local arenites and sandy carbonates. The lower member was deposited in a high-energy, shallow-marine subtidal to intertidal environment. Evidence includes sets of low-angle cross stratification (dunes), oncolites, oolites, and rip-up clasts. The middle member forms distinctive ledges and cliffs. The presence of thinly laminated algal stromatolites and relict structures seen also in the lower member indicate a subtidal to intertidal environment similar to that inferred for the lower member. The white color and coarse crystallinity may have resulted from recrystallization of the dark, finer grained dolomite that comprises the lower member. The upper member is characterized by lithologic variability. Thicknesses of limestone are greatest in the north, and decrease to only a few feet in the south. Quartz and other terrigenous minerals are scattered at intervals throughout the upper member, with a marker of sandy (arenaceous) dolomites at the base and near the middle and an increase of sand near the top also. The upper contact, with quartz-rich arenites (subarkosic quartzites) of the Worm Creek Member of tho St. Charles Formation, is gradational overall, but is sharp and planar in each section and readily located. In the upper member, algal mats trapped a varying but overall increasing influx of quartz and feldspar, probably in shallow subtidal environments, and vertically stacked hemispheroids suggest that depositional conditions may have included intertidal. Virtually all of the dolomite in the Nounan Formation must have formed by replacement of lime sediments by downward-moving high-magnesium brines. It is that these brines originated in restricted, shallow, subtidal evaporating basins, such as the Great Bahama Banks today, and associated supratidal flats. Lateral changes from limestone to dolomite overall and also in individual beds of the upper member indicate that the brines travelled laterally as well as vertically, and dolomitization may have been limited as much by prior diagenetic alteration and cementation as by the volume, concentration, and proximity of the brine itself.