A CLUSTER of fire-control and tree-thinning projects approved by forestry officials but never funded might have slowed the progress of the massive Rim Fire in California.

The blaze at the edge of Yosemite National Park in the Sierra Nevada mountains has scorched an area larger than many US cities, with some of the land in the location pinpointed by the US Forest Service for eight projects designed to clear and burn off brush and small trees, which fuel wildfire.

The projects, which Congress failed to fund, would have thinned woodland in roughly 25 square miles in the Groveland District of the Stanislaus National Forest, much of which was destroyed by the Rim Fire.

About 9000 acres were earmarked for fire prevention buffer zones in 2012, Forest Service chiefs said, but funding cuts for fire prevention coupled with stringent air quality standards, which limit burnings, hampered efforts to carry them out on a larger scale.

Last year, the service received funding to burn 449 acres in the Groveland District but did not reach that target.

The wildfire is the sixth-largest on record in California, and burned across 220,000 acres over the past two weeks and threatened to befoul San Francisco's main reservoir.