"Bonanza," the blockbuster 1959-73 NBC western series that helped spur the sales of color TV sets in America, is about to ride the Ponderosa again. The family-friendly Pax TV network, 32% of which is owned by NBC, is developing "The Ponderosa," a prequel to the old favorites, whose reruns, starring Lorne Greene, Michael Landon and Dan Blocker as the Cartwright clan are still a hit on Pax. "The Ponderosa," created by Beth Sullivan ("Dr. Quinn, Medicine Woman"), will be launched as a two-hour original movie, says the Hollywood Reporter. This, in turn, is expected to launch a series. David Dortort, the original creator and producer of "Bonanza," is also involved, as a consultant, reports the trade paper. This isn't the first time that the Cartwright family has been resurrected. In 1988 there was a TV movie, "Bonanza: The Next Generation," which starred John Amos and Michael Landon Jr. The senior Landon, who later gained greater fame on "Little House on the Prairie" (he died in 1991), played youngest Cartwright brother, Little Joe, on the original "Bonanza."