The Lake Tahoe Basin hasn’t been threatened seriously by wildfire since the Angora Fire in 2007. That was a relatively small blaze that broke out in June ignited by an illegal campfire. Despite burning only 3,100 acres, it torched more than 250 homes and caused a real panic. Fire crews contained the fire in just over a week, thanks to the small size and easy access to a blaze that was burning in a developed area with plentiful access.

Now the massive Caldor Fire is bearing down on the basin. As of Monday, August 30, it’s less than a dozen miles from the bustling town of South Lake Tahoe, and is already burning parts of the ski resort Sierra at Tahoe, which is also being used as a logistics staging ground for fire crews. It’s not unusual of course for fires to burn near Lake Tahoe, but it’s uncommon for one to encroach the lake itself by climbing then descending the granite ridges that ring the lake.

Schools throughout the Tahoe Basin are closed, in both California and Nevada because of smoke-choked skies. At least one hospital in the region has been evacuated. If you’re familiar with that area at all, perhaps you’ve made the drive from the Bay Area to South Lake, you might be shocked at size and speed at which the fire has blossomed, and the amount of lives that are being upended. Communities along Highway 50, the key route into the southern Lake Tahoe Basin, from Pollock Pines to Echo Summit at 7,300 feet, an hour’s drive, have been evacuated. This is not a fire burning in a largely untouched national forest—this is a relatively highly populated mountain area.

So far, the fire has marched steadily northeast, directly toward Lake Tahoe, from when it was first discovered August 14. Most days it has moved toward the lake at about a half mile per day, though yesterday it roared forward by two miles. The fire is burning mostly through abundant fuel sources: manzanita, cedar, and ponderosa pine. There is hope that as the fire pushed upward over Echo Summit, it will be slowed by more granite, less fuel on the ground, and giant stands of fir trees that aren’t as readily flammable as the brush below.

But that’s just the hope.

Just a few days ago, after a period of cooler temps and a slight uptick in humidity, crew leaders were optimistic they had the upper hand in the fire. Then temperatures soared and hot winds roared, and it’s a guessing game as to what the fire does next. Thousands of firefighters from across the country are on hand to patrol the blaze, to predict where embers might start spot fires across fire lines, to rush resources to likely hot zones. But still, topography is the best hope to halt the fire before it descends into Lake Tahoe proper and wreaks previously unseen havoc.

In this map provided by CalFire, the red areas are under mandatory evacuation orders, and the yellow are in evacuation warning.

Already the area is blanketed by smoke and ash and wariness. Small towns normally thronging with Labor Day tourist traffic sit dark and silent, with residents either shut inside against the smoke or long gone, businesses shuttered, and tourists absent.

As of late Sunday night, all people on the California side of Lake Tahoe, between the fire and clear to the water line, were under evacuation warnings. At any moment, the sheriffs and fire departments may start rushing through South Lake Tahoe, blaring horns and orders to leave.

Conditions from Monday through Tuesday night are expected to be blazing hot and windy.

The map below shows the fire progression though it can be slow to load. If it won’t load on your screen, visit https://arcg.is/1G8PeL.