On the knoll behind this marker, George Madeira built the first amateur astronomical observatory of record in California and there discovered the Great Comet of 1861 with a three-inch refractor telescope.

California Registered Historical Landmark No 715

Plaque placed by the State Department of Parks and Recreation in cooperation with the Stockton and Sacramento Astronomical Societies
November 17, 1968

Here in Volcano in 1860, miner and amateur astronomer George Madeira built California's first astronomical observatory of record and operated it for two years. Using a three-inch refractor telescope he studied the sun and moon, stars and planets, and other glories of the heavens, including the Great Comet of 1861.

California Registered Historical Landmark No 715

Plaque placed by the State Department of Parks and Recreation in cooperation with the Astronomical Societies of Stockton and Sacramento. Plaque placed first in 1968. Revised and relocated in 2004.