Twin Rocks, California

The same ground, surveyed 61 years apart. Drag the handle to wipe between them. Both sheets are United States Geological Survey originals; neither has been altered.

1920 1981

Matched by testing this settlement's coordinate against the published boundary of every sheet in the United States Geological Survey's historical collection. Each opens the scanned sheet at the Survey.

• 1920 USGS Cummings quadrangle1:62500
• 1952 USGS Leggett quadrangle1:62500, 3 printings
• 1957 USGS Ukiah quadrangle1:250000, 3 printings
• 1960 USGS Ukiah quadrangle1:250000, 2 printings
• 1969 USGS Tan Oak Park quadrangle1:24000, 3 printings
• 1981 USGS Covelo quadrangle1:100000, 2 printings

Regional context, not property-specific evidence. The federal wildfire occurrence database lists 86 fires within 5 miles of Twin Rocks between 1993 and 2018, burning about 13,047 acres in total. 7 started naturally. 4 were recorded as arson. Distance is straight-line from the map coordinates, so a fire counted here may appear on a neighbouring settlement's page as well.

The most recent of them, most recent first, with the day each was reported and the service that recorded it.

Settlements close enough to share some of these fires:

• Bowman Place
• Empire (historical)
• Tan Oak Park
• Cummings
• Leggett
• South Leggett

Every fire recorded in Mendocino County

Regional context, not property-specific evidence. The federal mineral resources record lists 12 workings within 5 miles of Twin Rocks: 7 occurrences, 4 prospects, 1 unknown. None of them still produces. What was taken out: Manganese, Clay, Chromium. Distance is straight-line from the map coordinates, so a quarry counted here may appear on a neighbouring settlement's page as well.

Every working recorded in Mendocino County

The eight closest, with where each one stands in the county. Distances are straight-line, computed from the Geographic Names Information System coordinates.

Matched on this settlement's Geographic Names Information System number rather than its name, so it cannot be a different place of the same name in another state.

This settlement is recorded in the Geographic Names Information System as feature 1724141. The sheet list is computed by point-in-boundary test against the United States Geological Survey's historical topographic inventory. Both are works of the United States government and carry no copyright under 17 U.S.C. 105.

Wildfire. Short, Karen C. 2022. Spatial wildfire occurrence data for the United States, 1992-2020 [FPA_FOD_20221014]. 6th Edition. Fort Collins, CO: Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2013-0009.6 Collected with United States Government funding and usable without additional permissions or fees.

Mines and quarries. USGS Mineral Resources Data System (MRDS) https://mrdata.usgs.gov/mrds/ A work of the United States government, no copyright under 17 U.S.C. 105.