Mackey was runner-up in last year's race and also finished second to Berkowitz in last week's Knik 200, but he isn't among the 54 mushers in this year's Copper Basin 300.
Aliy Zirkle, who finished runner-up in last month's Sheep Mountain 150, will compete, as will 2004 Iditarod champion Mitch Seavey.
The 269-mile race begins in Chistochina at noon. Mushers will make stops at Paxson Lodge, Meier's Lake Roadhouse, Sourdough Creek, Wolverine Lodge, Tolsona Lake Resort and Glennallen, before returning to Chistochina.
The race should end sometime Monday morning.
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