I recently flew Alaska Airlines to Arizona and checked a bike bag as regular luggage. This I believe is a recent change in the Alaska Airlines Policy
Below is the relevant content from their baggage policy page on their website -
Alaska Airline Baggage Policy
Individual sports equipment pieces
Each checked piece listed below is subject to our standard checked baggage fees and waivers. We’re glad to waive the oversize fee or overweight fee for the items listed in this section. If contents unrelated to the equipment are included, additional baggage fees may apply. Refer to our Checked baggage policy for checked piece charges and waivers.- Archery
- Bicycles
- Boogie boards
- Bowling
- Fishing Equipment
- Golf Clubs
- Hockey/Lacrosse Equipment
- Kiteboarding Equipment
- Pole Vaults
- Scuba Equipment
- Skateboards
- Skis/Snowboard
- Surfboards/Paddleboards
- Windsurfing Equipment
Just noticed you are from Portland - Howdy neighbor