Covered Bridge Series: Horton Mill Bridge Posted by Steven Norman on January 14, 2015 Posted in: Bridges, History, Travel. Tagged: Alabama, Blount County, Bridge, Covered Bridge, Horton Mill, Oneonta. 4 Comments The Horton Mill Bridge is a 220 foot long covered bridge which spans the Calvert Prong of the Little Warrior River in Oneonta, Alabama. Construction began in 1864 but it did not open until 1934. Horton Mill Bridge Oneonta, AL