The Waltham plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
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Waltham’s center stands about 320 ft above sea level. Within three miles the land runs from 100 ft to 330 ft, a difference of 230 ft: rolling country. The highest named summit within 15 miles is Bald Mountain, about 1,260 ft, 14 miles west.
Under the town center the state geologic map shows Devonian alkali feldspar granite (alkali-feldspar-granite), from the Devonian, 359 to 422 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 30×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Siltstone, phyllite. Age: Neoproterozoic to Ordovician, 445 to 1,000 million years old. About 10 mi of the line.
Alkali-feldspar-granite. Age: Devonian, 359 to 422 million years old. About 7 mi of the line.
Sandstone, limestone. Age: Ordovician to Devonian, 359 to 487 million years old. About 3 mi of the line.
Slate, schist, quartzite. Age: Middle Ordovician to Late Ordovician, 450 to 470 million years old. About 2 mi of the line.
Greenstone. Age: Neoproterozoic to Ordovician, 445 to 1,000 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in Waltham reaches the Atlantic Ocean by way of Old Meadow Brook and Mill Brook: about 7 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Waltham; river miles along the main stem, rounded.
