The fires have spread rapidly in recent days to burn 283,800 acres of land - an area nearly the size of Los Angeles.
Northern California is grappling with the largest wildfire in California history, breaking a record set only months earlier.
Where is the Mendocino Complex Fire?
The Australian crews were first sent to Boise, Idaho, for training at the National Interagency Fire Centre; and joined U.S. and Canadian firefighters in the field on Tuesday. This puts them at the number two spot on the list of largest wildfires in state history. That fire started in the Cleveland National Forest and evacuations in the nearby areas have been ordered, according to the Orange County Fire Authority.
They take aim at the biggest wildfires in two ways and in much of the same way the Department of Forestry and Fire Protection has for decades.
Several fire experts, however, said the comments don't address the main factor in fire severity: human-caused climate change. It doesn't mean that the fires have necessarily joined - and in the case of the Mendocino Complex Fire, the River Fire and the Ranch Fire have yet to meet. That fire ended up burning 281,893 acres before being contained. "The overload of dead and diseased timber in the forests makes the fires worse and more deadly".
This smaller blaze has consumed 48,663 acres and is considered to be 58% contained.
A number of complex fires fill the list of the top 20 largest wildfires in California history, including the 192,038-acre Klamath Theater Complex Fire near the OR state line in June 2008.
It has claimed more than 1,600 buildings, a lot of them homes.
Another major wildfire is tearing through California and it's growing at a phenomenal pace.
Water, used in protecting homes and other structures and for dumping on flames from airplane tankers and helicopters, is critical but secondary to the larger manual efforts of clearing unburned vegetation to remove it as potential fuel around a fire's perimeter.
More than 11,000 structures are listed as being threatened by the fires.
No injuries or deaths have been reported among firefighters or civilians. Officials have confirmed that six people, including two firefighters and a woman and her two great-grandchildren, have died.
Here & Now's Robin Young speaks with Hanna Kuyper of Redding, who lost her home in the fire.
The Mendocino Complex Fire grew under conditions ripe for an aggressive, fast-moving wildfire.
The second portion of Trump's tweet, that California "Must also tree clear to stop fire spreading!", is also confusing. Blazing temperatures during the day have exacerbated the wildfire. You warm the soils, you dry them out, you get worse drought. The Carr Fire is now the 12th largest fire recorded in the state.