The Maryland and Pennsylvania Railroad, known as the Ma & Pa, ran 77.2 miles from Baltimore to York and became known as Harford County's Railroad because it passed through the center of Harford County. Its winding, hilly route had 476 curves, 92 percent of its track on an up or down grade, and only two level sections, including a one-mile stretch from Bel Air to Bynum. Its numerous bridges, viaducts, and trestles gave it a scenic appeal that attracted rail enthusiasts and photographers. The line's predecessors used narrow gauge track common in the late 19th century, but conversion to standard gauge allowed interchange with other railroads and the use of faster, more powerful equipment. Maryland Central Railroad reached Bel Air on June 21, 1883; the Maryland Central Railway and York & Peach Bottom Railway merged in 1891 to form the Baltimore & Lehigh Railroad; the Baltimore & Lehigh Railway converted the Baltimore-Delta segment from narrow gauge to standard gauge on August 23, 1900; and on February 12, 1901, the Baltimore & Lehigh Railway and York Southern Railroad merged to form the Maryland & Pennsylvania Railroad. The Ma & Pa reached its peak in the 1920s and early 1930s, when it owned as many as sixteen steam-powered locomotives, numerous box cars, and several gasoline-electric motor cars for passenger service. By running directly through Harford County, it gave farms and canneries, including Spenceola Farms at Forest Hill, easy access to markets in Baltimore and York, carrying freight such as tomatoes, sweet corn, potatoes, and milk, and it also carried mail until September 1954. During the Great Depression, gross revenues were halved in three years, and although scenic steam trips remained popular, the railroad never fully recovered. The railroad ordered its first diesel locomotives in November 1946. On August 31, 1954, the last passenger train on the line left Baltimore for a round trip to York, made up of two gas-electric motor coaches, a rented coach, and a baggage car pulled by Diesel engine No. 81, and about 100 people gathered on the North Avenue Bridge to watch it pass below on its final run. On June 11, 1958, after five years of financial losses, Diesel engine No. 82 made the last run to collect loaded and empty cars, after which the Baltimore to Whiteford section was abandoned. Today, the Ma & Pa Heritage Trail follows part of the original railbed.