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A rare and detailed early road plan showing Sonoma County during a key moment in the transition to automobile-era infrastructure. Issued in 1918 by County Surveyor M. P. Youker, the map outlines a county-wide program of proposed road improvements, using hand-applied color to indicate the planned type of construction: red for Class “A” concrete roads, yellow for Class “B” water-bound macadam, and blue for Class “C” graded and graveled surfaces. These classifications reflect contemporary national standards promoted by the Bureau of Public Roads and adopted by counties in the wake of California’s 1910 and 1915 highway bond measures.

The map reveals a clear hierarchy of investment. A solid red corridor runs north–south from the Marin County line through Petaluma, Cotati, Santa Rosa, Windsor, and around Healdsburg. Branching from this are secondary and local roads leading west to Bodega Bay and the Russian River resorts, east to the Sonoma Valley, and inland to smaller settlements and agricultural areas.

A note near Guerneville records that the bridge across the Russian River was open only from June to November, capturing the seasonal isolation that characterized travel in the region before year-round crossings were built. The map preserves this transitional moment, just before the postwar California Highway Bond Act of 1919 and the rise of federal aid would begin to transform rural infrastructure at a much larger scale.

Youker’s map is also a significant historical document for its local detail. It plots township-and-range sections, creeks, peaks, rail lines, and historic land grants. The application of the construction classes was done by hand, suggesting that this copy may have served a working role within the county office or another small-run official setting.