Flying tiger's right. Mesaba has RJ85s, which is a newer version of the BAe 146-200. As far as I can remember, Hawker-Siddely, the original manufacturer of the BAe 146 (it was originally designated the HS 146, before the merger of HS and Vickers to form British Aerospace)couldn't produce a twin-engined regional jet at the time in the late '70s that would be quiet enough to meet increasingly strict noise requirements of airports. So four relatively weaker turbofans were actually quieter than two with greater power.
It was also made to operate from hot-and-high airports in Third World countries, that's one of the reasons for it having four engines. Jet aircraft typically require more fuel to takeoff and fly in hot weather or at high altitudes, both conditions which make air less dense and therefore make jet engines less efficient. The BAe 146 didn't sell as well as anticipated in Third World countries, possibly because it is expensive to maintain. But there are quite a few BAe 146s operating in Australia, especially in hot conditions, but no Avro RJ85, though. There are 10 BAe 146s (AirBC and Air Nova) in operation in Canada, so I've flown on a few of them, mostly on AirBC. There are a few other BAe146/Avro RJ operators in North America besides Mesaba, such as Air Wisconsin(United Express) and also several in Europe, where they found the biggest market.