Abstract Johnstown, Pennsylvania, has long been associated with flooding due to major floods in 1889, 1936, and 1977. The most famous of these floods, the Johnstown Flood of 1889, led to more than 2200 deaths and was the result of the catastrophic collapse of the South Fork Dam. This privately owned dam was located on the South Fork of the Little Conemaugh River, ~14 mi (23 km) upstream of Johnstown. The dam changed ownership multiple times since its initial construction and had been improperly rebuilt and maintained after partial breaches. It was the final failure after a wet spring and heavy rainfall that resulted in death and devastation along the Little Conemaugh River valley from South Fork to Johnstown. This field guide presents the history of the South Fork Dam and incorporates recent studies that examined the timing of the flood and failure of the dam itself. The field trip begins at the origin of the flood at the South Fork Dam and largely follows the path of the flood down the valley to Johnstown with stops at sites impacted by the flood wave, as well as sites that demonstrate a response to the flood.