Harris' visit will follow by a day the arrival in the state of President Donald Trump.
Authorities say almost all the dozens of people reported missing after a devastating blaze in southern OR have been accounted for, but the fires have killed 35 people from California to Washington state.
The three Democratic leaders of California, Oregon and Washing blamed the states' dire conditions on climate change.
Los Angeles Mayor Eric Garcetti accused Trump of perpetuating a lie that only forest management can curtail the massive fires seen in recent years.
Trump is set to arrive late morning in McClellan Park, where heads of California's emergency services will brief him on the fires.
The blazes have burned almost five million acres (two million hectares) across the US West, torching an area roughly the size of the state of New Jersey, with fears the death toll may rise.
California has seen 3.3 million acres burn - an annual record, with more than three months of the fire season still to come - and over 4,100 structures destroyed.
At least 10 people have been killed in OR, according to the office of emergency management. Officials have said dozens of people are missing and warned that the death toll could rise. In California, 24 people have died, and one person was killed in Washington state.
What are the politicians saying?
At least 35 active fires were burning in the state, as drought conditions, extreme temperatures, and high winds created the "perfect firestorm" for the blazes to grow, Governor Kate Brown told CBS news on Sunday. We saw very cold, hot temperatures.
"It's apocalyptic", Washington state Governor Jay Inslee told ABC's "This Week".
"We submit the science is in and observed evidence is self-evident: that climate change is real and that is exacerbating this".
At an election campaign event in Nevada on Saturday, President Trump said he was praying for everyone throughout the West Coast affected by the wildfires.
Forest management, which includes tree thinning and brush clearing, is costly, labor-intensive work that is effective in reducing fuel for wildfires.
"They never had anything like this", he said.
"There has to be strong forest management", he said.
Mr Trump has previously called climate change "mythical", "non-existent", or "an expensive hoax" - but has also described it as a "serious subject".
What role is climate change playing?
But he said the overwhelming cause of the problem is far bigger.
Nine of the world's 10 warmest years on record have occurred since 2005, and the United Nations warned this week that the five years from 2016 until this year will very likely be the hottest such period yet recorded. He asked the president to "please respect" many Californians' and Democrats' views that there is a climate crisis.
Standing amid ash and ruin on Friday, California Gov. Gavin Newsom said the historically devastating fires that have ravaged his state in recent years stand as a case study for the reality of the scientific warnings around climate change and blasted the "ideological BS" of those who would deny it. In Oregon, the spate of fires burned nearly twice the amount of average annual losses in a week.