AZ-UT: Mile 143 + 64 chains: Antelope Island

AZ-UT Mile 143 Brown Monument on Antelope Island looking west toward Wahweap

Brown’s triangulation station on Antelope Island, looking west.

On Antelope Island, Lake Powell, on the Arizona-Utah line through the high red desert, with Wahweap, Arizona in the distance. Here, Surveyor Brown’s 1934 Triangulation Station sits as a stolid witness to the subtle geological changes in the nearly-Martian desert surface while major climate upheavals pull on the theatre set backdrops: Lake Powell’s water level in 2018 was 107 feet below ‘full pool’, indicated on the 1985 map below. Brown’s triangulation station, placed before its location could be called an island, long before the Glen Canyon dam was built, faced the implacable rise of Lake Powell: in 1985 the monument sat on a peninsula; now the lake has ebbed away.

Looking east at the Brown monument on Antelope Island. Navajo Mountain rises in haze due east of here.

Antelope Island Survey Monument stamped “Brown” and “1934" — Antelope Island Survey Monument stamped “Brown” and “1934″

37⁰ 0.0940′ North 111⁰ 27.1937′ West

The 1934 border monument named Brown appears on a peninsula, surrounded by water, on the USGS map. — In the lower left corner, the 1934 border monument named Brown appears on a peninsula, surrounded by water, on the USGS map.

A 2026 Google Earth image showing the extent of Lake Powell’s shrinkage

On the east side of Antelope Island, approximately Mile 144. Navajo Mountain remains a gnomon on the horizon, 31 miles away.

Looking east, from the east side of Antelope Island, with Navajo Mountain in the distance, a blue hump on the horizon; the borderline passes over the mountain’s southern flank. Near the right edge of the image, the Navajo Generation Station’s stack (subsequently demolished) merges with the storm cloud above it.

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