The Middle Fork originates at Helen Lake in the high Sierra, near Muir Pass in Kings Canyon National Park. From its headwaters at above sea level, it descends rapidly east down Le Conte Canyon, turning south at Big Pete Meadow. It passes the Le Conte Ranger Station and receives Dusy Creek from the east and then the much larger Palisade Creek, also from the east, a short distance downstream. Flowing south, it enters a narrower canyon where it drops over a waterfall known as Devil's Washbowl. It receives Cartridge Creek from the east, then turns southwest through Simpson Meadow, a broad subalpine valley at about elevation, where it receives Goddard Creek from the north.