Photos: Kaltag, Iditarod's final Yukon River checkpoint

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Jeff King at the Kaltag checkpoint on Saturday, March 14, 2015.

In frigid cold well before dawn, Aliy Zirkle and her 14 dogs left the mighty Yukon River and headed west toward the stretch run of the Iditarod Trail Sled Dog Race.

Zirkle pulled out of Kaltag at 2:48 a.m., after stopping in the village just 14 minutes to give her dogs a quick snack.

Although she is likely to stop and rest during the rugged 85-mile haul to the Norton Sound coast, she started with a lead of nearly two hours over four-time champion Jeff King, the second musher out of Kaltag. Aaron Burmeister was 12 minutes behind King, and then came the musher who looms, perhaps, as the biggest threat in the 43rd race to Nome -- Dallas Seavey. The defending champion was on the trail at 5:35 a.m. and his 14 dogs appeared to be moving fastest among the frontrunners. They made the 50-mile run from Nulato a full hour faster than Burmeister and about 40 minutes faster than King and Zirkle. If that speed holds up as the frontrunners move down the Seward Peninsula towards Nome, it could prove decisive.

READ MORE: Zirkle takes Iditarod lead out of Kaltag, heads for the coast