“(In 1901) a new racetrack and an amusement park just across the city line brought a lot of city folk out west. The racetrack straddled the boundary between the country and the city on the north side of Delmar. The entrances to the grounds, or gates, were the source of the names of two streets. Delmar Gardens, at the loop of the Delmar line, was one of several amusement parks or resorts at the ends of the street car lines....Delmar Gardens boasted of “magnificent theaters presenting star performers in opera, dram and vaudeville.” The park had a variety of restaurants where a visitor could even get caviar...A series of wet summers around World War I and changing tastes, forced the closing of most of the street car line amusement parks including Delmar Gardens.” From Legacy of Lions, A History of University City, 1981, Historical society of University City, St. Louis, MO.
The race track itself closed down after 1905 because of a crackdown on gambling.
“Delmar Gardens (Amusement Park) was located along Delmar Boulevard between Kingsland and Skinker. Built before the St. Louis World's Fair, it was a popular entertainment spot until 1911. In addition to the scenic railroad, it had a large merry-go-round, music halls, beer gardens, band pavilions, picnic areas, theaters and a nearby race track. The entrance and exit to the Gardens gave their names to the present Eastgate and Westgate Avenues.” From A University City Album, The Citizens Committee for the Seventy-Fifth Anniversary
EDIT: A video, CALOP's University City: The First Century, available from the University City Public Library, is a great brief history of the origins of University City and Delmar Loop: