Surficial Geology and Hydrogeology of the Town of Randolph, VT
by Stephen Wright, Fred Larsen, George Springston and Marjorie Gale, 2011, VGS Open File Report VG11-2

Click here for a report on the geology and hydrogeology of Randolph, VT by Stephen Wright
Click here to download digital database (geodatabase format).

Surficial Geologic Map of the Town of Randolph, Vermont by Stephen Wright, Fred Larsen and George Springston, 2010, Open File Report VG10-2

Hydrogeology of Randolph, Vermont by Stephen Wright and Marjorie Gale, 2011

Summary of Major Findings: Randolph Vermont Surficial Mapping
Bedrock
Bedrock crops out widely across the area above the elevation of the glacial lake that occupied the valley (~740–770 ft). No striations or other direct evidence of glacial abrasion were observed on any outcrops, even where freshly exposed. No bedrock outcrops were found in the valley suggesting that the bedrock surface is deeply buried. This is also supported by well log data and the depth to bedrock is contoured on the isopach map.

Glacial Till
Glacial Till in the Randolph area is ubiquitous in areas above the elevation of the glacial lake that occupied the valleys (~740–770 ft) and directly overlies bedrock. In all exposures observed it is gray, compact, and contains a large percentage of fine (clay, silt, and sand-sized) sediment. In most areas till thickness is less than 10 m, but exposures in some landslides and well logs indicate that till has accumulated to thicknesses of 20 to 30 m in restricted areas.The isopach map shows depth to bedrock or thickness of the overburden in Randolph based on well log data and field mapping.

Ice-contact Sediments
An segmented esker system occurs in the Second Branch of the White River valley and is apparently continuous with one on the northern side of the drainage divide in the same valley occupied the the Steven’s Branch of the Winooski River. In one area north of East Randolph exposures in pits are good enough to show that this esker is braided. This esker is the primary source of sand and gravel in the Second Branch Valley. In the southern part of town this esker is largely buried by younger glacial lake sediments.

Glacial Lake Sediments
Glacial lake sediments are widely distributed at elevations below 740–770 ft and overlie bedrock, till, and ice-contact sediments. These sediments were deposited in an arm of Glacial Lake Hitchcock, the large glacial lake that occupied the Connecticut River valley. Surface exposures consist mostly of varved silt and clay, but also include very fine sand. Sections generally fine upwards from underlying till or ice-contact sediments. Several good sections were observed, but no detailed measurements were made. At least two areas are interpreted to be deltas. Glacial lake bottom sediments frequently occur at elevations near the surface elevation of the lake, sometimes overlain by a thin cover of alluvium, indicating that these sediments largely filled in the lake.

Alluvium
Old stream alluvium occurs on terraces and fans deposited on top of lake bottom sediments at elevations ranging from the old elevation of Glacial Lake Hitchcock to the modern stream elevation. These sediments range in thickness from less than half a meter to 2–3 m and have, in some places, been used as a source of sand and gravel.