A fast-growing wildfire in northern California led to evacuation orders, a highway closure and a bike event cancelation — as the threat of "dry lightning" prompted red flag warnings to be issued across the state.

The big picture: The Tamarack Fire, south of Lake Tahoe near the Nevada border, is among 70 large fires burning across over a million acres in the U.S., including nine in California. It comes as another heat wave grips the country, this time with the intensity focused on the northwest and northern areas.

A Red Flag Warning has been issued due to the threat of dry lightning starting late Sunday morning and lasting through Monday afternoon.

Be sure to stay weather aware and have a plan if a fire starts in your area.#CAwxpic.twitter.com/F1uJ1QATKc

— NWS Bay Area (@NWSBayArea) July 17, 2021

• Many of the wildfires started amid an unprecedented heat wave that scientists say was driven by human-caused climate change.

What's happening: The Tamarack Fire was being driven by "gusty winds" and "critically dry fuels" as it was burning uncontained near the town of Markleeville, per a statement from Humboldt Toiyabe National Forest. It has razed some 21,000 acres after being ignited by lightning on July 4.

• Mandatory evacuation orders were issued for several nearby areas, forcing Death Ride, to cancel its extreme bike event through the Sierra Nevada Saturday, according to a statement posted to its website.
• "The fire left thousands of bikers and spectators stranded in the small town and racing to get out," AP reports. The blaze also saw part of Highway 89 close, at the intersection of Highway 4.
• A red flag warning was also in effect for the Bootleg Fire in southern Oregon, currently the largest wildfire in the U.S. — which grew to 281,208 acres and was 22% contained Saturday, per InciWeb.

By the numbers: 17 wildfires were burning in Idaho, 13 in Montana, nine in Oregon, seven in Washington state, six in Alaska, four in Arizona, two in Wyoming, and one apiece in Colorado, Utah and Minnesota, National Interagency Fire Center statistics show.