There could not be a less hospitable spot for a major wildfire than the Merced River Canyon near Yosemite National Park. In July and August of 2008 the Telegraph Fire burned over 50,000 acres and claimed dozens of homes in and around Mariposa just down canyon from where the Motor Fire is raging.
The Motor Fire has burned 3,000 acres in two days and firefighters are still in the early stages of formulating a plan of attack. Initial reports had the fire burning on both sides of Highway 140 and the Merced River which would give the fire two distinct heads and directions. Maps are showing the fire burning mostly on the north side of the river and highway. The Telegraph Fire burned on both sides of the canyon as it raced upstream towards Yosemite which complicated suppression activity. Firefighters could not use the massive Merced River as an anchor.

Motor Fire and Proximity to Yosemite Nat Park

The GeoMac image above highlights the perimeters of recent fire activity including the Telegraph to the west and the Grouse and Big Meadow fires to the east. The Big Meadow and Grouse burns will act as a pair of defensive tackles blunting (somewhat) the eastern progression of the Motor Fire. There is no recent fire history north of the Motor so a run to Highway 120 is entirely possible.

A look at the area of responsibility shows this will be a Forest Service show with Cal Fire responsible for only a couple of strips of land and property along the river and highway. Cal Fire was responsible for suppressing the Telegraph Fire and at one point had 4,500 firefighters, 30 or more fixed wing aircraft and helicopters, 61 fire crews and 101 fire engines on scene. It will be interesting to see how many resources the Forest Service puts in use.