title: Geology of the East-Central Part of the Malad Range, Idaho
Creators: name: Prammani, Prapath
Publisher: name: Utah State University
Year: 1957

description: Purpose and Scope
During recent years geologic investigations have been made in various parts of northern Utah and southern Idaho. In the Cache Valley area. the Bear River Range which bounds the east side of the valley has been studied and mapped. On the west side of the valley, the Wellsville Mountain and the southern part of Malad Range have also been studied. Still, little is known about the east-central part of the Malad Range. The study of this area will give additional information to the over-all picture of the geology of the region. The purpose of this thesis is threefold. The first purpose is to make a reconnaissance geologic map of the area; the second is to interpret the local structure in terms of the regional structure; and finally, the third purpose is to correlate the local stratigraphy to that of the region.
Location and Accessibility
The map area is located geographically at longitude 112°06' 1 west and latitude 42°02' north and is in the northeast corner of the Basin and Range Province. It also lies in the east-central part of Malad Range which separates Cache Valley from Malad Valley. The area extends north­ward about 5 miles from the Utah-Idaho state line and has the average width of 5½ miles. It lies in Township 16 South and Range 37 Fast, Boise base and meridian, Franklin County, Idaho.
The small town of Weston. located about 5 miles east of the present area. is about 25 miles north of Logan on the Idaho highway 35. The im­proved road from Waston to Halad Valley, intersecting U.S. highway 191 about 5 miles north of Malad City, passes through the northern part of this area. A graded road leading northward from the town of Clarkston, which is about 20 miles northwest of Logan, goes through the east margin of the map area. Access to the area from the main road is provided by dirt roads which are nearly impassable during the wet period.
Previous Investigations
The Malad River was named by Donald McKinsey in 1819 (Walgamott, 1927). Malad in French means sick. This name was probably given to the town and mountain range in a later period. In 1871 the geologic explo­ration group under the leadership of Hayden (1871, p. 20) took the trip from Ogden, Utah, to Fort Hall, Idaho, en route to Yellowstone. His party passed through Cache Valley. Hayden described the mountain range on the west side of the valley which separates Cache Valley from Malad Valley as composed of the same kind of rocks found on the east side of the valley. Bradley (1872, p. 199-200), in reporting his trip along the Wasatch Mountains from Ogden to Fort Hall, gave a description of the rocks on both sides of the "Gates" and the Tertiary limestone in Junction Hills west of Cache Valley. He also mentioned that the Tertiary rock lies unconformably upon the older limestones. In 1877 the geologists of the Green River Division under Peale (1877, p. 521) traveled along the east side of the Malad Range and passed through the area of present study on their way from Franklin, Idaho, to Ogden, Utah. They recognized that the isolated hills that form the Malad Range seem to have formed the islands that rose above the old lake, and that the younger Tertiary rock is de­ posited against the old Paleozoic formations. Peale mapped the central part of Malad Range consisting of Silurian and Tertiary rocks (Hayden, 188)). Gilbert (1890, p. 351), working on the geology of Lake Bonneville, described briefly the fault scarp at Clarkston which followed the west margin of Cache Valley to the north and probably passed through the present study area. As a result of work by Walcott (1908. p. 5-9. 191- 200) on the Cambrian section of northern Utah and southern Idaho, the formations of the Cambrian system in this area were named and studied. Work by Richardson (1913) on the geology of the Randolph quadrangle com­pleted the remaining Paleozoic sections. Mansfield (1927) studied the geology of southeastern Idaho, giving useful information on the stratigraphy and structure of the region. To the north of the map area, the Pocatello quadrangle was worked by Ludlum (1942) and the pre-Cambrian rocks of that area were described and defined by him. Hanson (1949) studied and mapped the southern Malad Range. The Garden City limestone. which is prominent in the present area, was described by Ross (1951) with emphasis on its occurrence in northeastern Utah. Piper (1924) investigated the possibilities of petroleum in Power and Oneida Counties, Idaho, for the Idaho Bureau of Minas and Geology; and mapped the present area as consisting of undifferentiated Cambrian, Ordovician, and Tertiary rocks.
Field Work
The field work for this thesis was undertaken during the summer of 1956. The data obtained were plotted on acetate paper laid over United States Soil Conservation Service aerial photographs (scale 1:20,000). As a base map, the United States Forest map (scale 1:250.000) of the Caribou National Forest was used. The base map was enlarged from the original scale to the scale of the aerial photograph. Later the data were transferred to a base map of the same scale. A few control points were selected from the section corners as available.
Stratigraphic sections were measured with Jacob's staff, a 100-foot steel tape, and a Brunton compass. The data were changed into stratigraphic thickness with the aid of Mertie's chart (1947). Rock samples and fossils were collected for study in the laboratory. The color of rock samples was determined in the laboratory with the rock color chart of the National Research Council.