A farmer and his two sons, aged 8 and 10, were at his fishing camp on August 13, 1947. At about 1300 hours, he went to look for the boys, having sent them to the river for some tape from his boat. He noticed an object some 300 feet away, 75 feet above the ground. He saw it against the background of the canyon wall which was 400 feet high at this point. It was hedge hopping, following the contour of the ground, was sky blue about 20 feet in diameter and 10 feet thick, and had pods on the side from which flames were shooting out. It made a swishing sound. The observer stated that the trees were highly agitated by the craft as it passed over. His two sons also observed the object. No one saw the object for more than a few seconds.

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Entry on this case from Brad Sparks' "Catalog of 1,500 Project Blue Book Unknowns":

Aug. 13, 1947. Snake River 6 miles W of Blue Lake Ranch, 9 miles NW of Twin Falls, Idaho. 1 p.m. A. C. Urie on land and 2 sons Billy and Keith 300 ft away in a boat, all on the S side of the river or river bank looking to the N, saw a squeezed or elongated straw-hat shaped sky-blue object about 10 x 10 x 20 feet, with pods on the side emitting flames, about 1/2 mile away fly towards them down the canyon at 1,000 mph E-W at 75 ft height, with a contour following motion up and down over uneven terrain, trees swaying underneath with a circular motion, disappearing with a swish sound. Urie was about 300 ft from the object which was about level with him about 75 ft above the river, and silhouetted against the canyon wall 1,200 ft away, disappearing behind a hill about 1 mile away. Object was at about 45° elevation to the boys on the river below him, disappearing behind trees. (Battelle Unknown No. 9; FOIA; FUFOR Index)