1. On May 15, 1901, the town of Ralston was founded in Noble County. Ralston was established on land that had formerly belonged to the Ponca Tribe and was named after Albert J. Ralston, who was a prominent Oklahoma businessman and politician.

2. May 15, 1910, marked the opening of the Oklahoma State Capitol building in Oklahoma City. The impressive structure was designed by renowned architect Solomon Andrew Layton and is listed on the National Register of Historic Places.

3. On this day in 1939, the Oklahoma City Zoo opened to the public. The zoo is home to over 1,200 animals from around the world and offers a variety of exhibits and educational programs for visitors of all ages.

4. May 15, 1957, was a significant day in Oklahoma's civil rights history. Oklahoma Governor Raymond Gary signed a landmark piece of legislation that prohibited segregation in public schools, making Oklahoma one of the first states in the country to desegregate its schools.

5. On May 15, 1988, the first annual Red Earth Native American Cultural Festival was held in Oklahoma City. The festival celebrates the rich cultural heritage of Oklahoma's Native American tribes and attracts thousands of visitors from around the world each year. In addition to traditional dances, music, and art, the festival also features a parade and a powwow.