Which Western series ran for 20 seasons on CBS, from 1955 to 1975?

In 'Justified', which actor played U.S. Marshal Raylan Givens? In 'Deadwood', in which territory is the series set? In 'Lonesome Dove', which two actors played the retired Texas Rangers? In 'Gunsmoke', in which Kansas town is the series set? In 'Bonanza', what is the name of the Cartwright family ranch? In 'Dallas', what is the name of the Ewing family ranch? In 'Dynasty', which actress played Alexis Colby? In 'Knots Landing', from which show did the series spin off?