FOG BLOG U.S. NEWS LOG: YOSEMITE NATIONAL PARK UNDER SEIGE BY WILD FIRES, SEQUOIAS UNDER THREAT!

Yosemite Park sequoias under threat from wildfire amid western U.S. heat wave Meanwhile, Texas residents are being asked to conserve power as heat threatens electricity grid High temperatures in the southwest and western U.S. were posing a challenge to firefighters in California and Utah, with Texas regulators warning of potential rolling blackouts on Monday.

In California, a heat wave was developing but winds were light as firefighters battled a wildfire that poses a threat to a grove of giant sequoias and a small community in Yosemite National Park.

The Washburn Fire on the western flank of the Sierra Nevada mountains had scorched about 5.8 square kilometres by Monday morning, an increase of about 120 hectares overnight, according to an incident update.

The fire was a threat to more than 500 mature sequoia trees in the park's Mariposa Grove and the nearby community of Wawona, which has been evacuated.

The area in the southern portion of Yosemite was closed to visitors but the rest of the national park remained open.