(Salem, OR)  --  The League of Oregon Cities says it plans to ask the state Legislature next year to allow city governments to implement local taxes on marijuana.  "The Oregonian" reports at least 70 cities, including Portland and its suburbs, want to be allowed to pass their own taxes on pot.  The recreational use of marijuana was approved by Oregon voters in the November 5th election, but Measure 91 prohibits local taxes.  Sponsors of the measure say local taxes could drive up the cost of legal marijuana to the point of encouraging pot users to continue buying on the black market.