Added information from BeerSmith
Ahtanum is an aroma/flavoring hop variety that is similar to Cascade or Amarillo. It has a citrus and floral character much like cascade with the addition of some piney or earth notes. Grapefruit quality is more forward in than in cascade as well. Alpha acids are lower than cascade at 4 to 6.5% AAU making Ahtanum a good choice for a flavor addition when you do not want to impart quite the bitterness of cascade or amarillo.
Beer styles suited for Ahtanum include American APA, American IPA, Light lagers. I also think they would be nice in a brown ale, but have not tried this out myself. [http://www.brew365.com/hops_ahtanum.php Brew365]
*Typical Use : Aroma/Flavor*Alpha Acid : 5.7 to 6.3% [http://www.midwestsupplies.com/us-ahtanum-pellet-hops.html Midwest Supplies], 4 to 6.5% [http://www.brew365.com/hops_ahtanum.php Brew365]
*Beta Acids: 5.0 to 6.5% [http://www.midwestsupplies.com/us-ahtanum-pellet-hops.html Midwest Supplies]
*Origination : USA*Characteristics : Floral, citrus, piney, Sharp*Styles : American Ales & Lagers*Similar Hops : Cascade, Amarillo*Commercial Examples : Stone Brewing - Arrogant Bastard, Sierra Nevada - Celebration