The Alma 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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Alma’s center stands about 4,880 ft above sea level. Within three miles the land runs from 4,870 ft to 6,110 ft, a difference of 1,240 ft: steep hill country. The highest named summit within 15 miles is Willow Mountain, about 10,790 ft, 13 miles east.
The section below crosses 10 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 4×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Unconsolidated. Age: Pleistocene to Holocene, less than 0.1 million years old. About 6 mi of the line.
Conglomerate-sandstone, volcanic. Age: Late Oligocene to Pleistocene, 0.1 to 28 million years old. About 4 mi of the line.
Rhyolite. Age: Early Oligocene to Late Oligocene, 24 to 29 million years old. About 3 mi of the line.
Basalt, andesite, dacite. Age: Middle Eocene to Late Miocene, 11 to 38 million years old. About 3 mi of the line.
Basaltic-andesite, andesite. Age: Late Oligocene to Early Miocene, 22 to 26 million years old. About 2 mi of the line.
Felsic-volcanic. Age: Late Eocene to Early Oligocene, 31 to 36 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 4 smaller units along the line are not listed.
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 Alma reaches the Gulf of California by way of the San Francisco, the Gila and the Colorado: about 670 river miles.
460 miles of the trip are on the Gila.
Often dry. About 40% of the way is mapped as streams that run only after rain or snowmelt; the water makes the whole trip in floods.
Seldom reaches the sea. Dams and canals now take nearly all of the Colorado before its old delta in Mexico.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Alma; river miles along the main stem, rounded.
