Registering for Alaska Airlines Mileage Plan with a California address using this link will provide you with a $50 discount on an Alaska Airlines flight.

• Register for Mileage Plan as a California resident by October 26 (though it’s conceivable that Alaska could pull the offer earlier).
  
• You’ll receive an email with the $50 discount within 48 hours of registration.
  
• Discount must be used for the Mileage Plan member’s travel only.
  
• Valid for travel between September 5 and November 10 for travel departing from California, and excludes travel to Prudhoe Bay.

It’s the requirement that travel must originate in California that presumably helps them limit non-California residents from registering with a California address. Though I wonder how well that will work, since Alaska generally prices roundtrips simply as two one-ways and the terms and conditions don’t state a roundtrip requirement, one could use the discount on a trip to California as well — buying a one-way to California and using the discount on a one-way return flight should work.