Back when SkyWest was operating as the Delta Connection in California with Metro III and Brasilia turboprops, it was easy to earn DL miles on short trips within the state. For example, a round trip flight between San Luis Obispo and San Diego via a connection both ways at LAX would earn 4000 miles or 1000 miles per segment SBP-LAX-SAN r/t.

As for redeeming miles, I remember when for a mere 100,000 CO OnePass miles one could fly round trip between Houston and Paris via Continental on the domestic legs and Air France on the transatlantic legs. And the AF legs were round trip on the Concorde.