UPDATE, 12:20 p.m. Wednesday: Fire officials said on Wednesday that the country's current largest blaze, the Martin Fire, is about 48 percent contained. They also updated the size of the fire to about 686 square miles. 

Investigators now believe the fire was human-caused, possibly by campers over the Fourth of July. The fire started July 5.

The fire remained active Tuesday under the combination of high temperatures, low humidity and variable winds, according to the Bureau of Land Management. But fire official are hopeful as resources continue to increase containment.

The current containment estiment is July 20.

Original story

PARADISE VALLEY, Nev. (KLIX) – A wildfire near Paradise Valley has been named the largest blaze currently burning in the Upper 48.

The Martin Fire, estimated at 443,000 acres – or 692 square miles – started in the early morning hours of July 5. A cause has yet to be determined, but the fire has drawn a number of crews and equipment to the arid Nevada landscape. The blaze on Tuesday was listed being only 35 percent contained.

Fire officials say crews made significant progress on both the eastern and western flanks and along the northern and southern borders. As flanks are secured, additional resources will be able to attack the head of the blaze.

Those resources continue to be mobilized. On Tuesday, 634 firefighters were devoted to fighting the fire, not quite one for every square mile, including 17 crews, nine helicopters, 25 engines, eight dozers, and 10 water tenders, according to the Bureau of Land Management.

The fire, which is burning in a swath from the Santa Rosa Range to the South Fork of the Owyhee River in north-central Nevada, is burning in grass, sage brush and small stands of timber.