[ILLEGIBLE], [ILLEGIBLE] - Incident Number: [ILLEGIBLE]Date unknown

On September 23, 1948, two men standing near San Pablo, California witnessed an unusual aerial object at midday. One observer described it as a large, translucent, buff-gray object resembling a four-engine bomber in size, with a spherical center portion that undulated and had appendages fore and aft like an amoeba. The second observer described the same object as resembling a "vegetable crate" covered with translucent material. Despite standing side by side, their descriptions contradicted each other sharply.

The investigator noted that one observer was far-sighted but wore no glasses, while the other was over seventy years old, needed glasses to read, and wore none at the time of the sighting. The Air Force concluded that while some object was indeed seen, the contradictory descriptions rendered the evidence useless. The file notes that a balloon, cluster of balloons, aircraft, or cloud could have been the stimulus for the sighting.

Weather analysis revealed that a Navy rawinsonde and Weather Bureau pilot balloon sounding had been released approximately one hour prior to the sighting. However, wind flow was westerly at all levels from the surface to 15,000 feet, which would have precluded either balloon drifting north to the San Pablo area. Both witnesses also agreed the object was traveling at high speed, but winds in the region did not exceed 24 knots. The Air Force concluded the object was not a balloon.

A second incident on the same date involved a Colonel and a Mr. observing an object from Castro's Ranch, 4 miles east of San Pablo and 4.1 miles south of Pinole. The Colonel described the object as approximately the size of a large four-engine bomber, shaped like an amoeba with three appendages forward and two aft that seemed to flap or oscillate while the center remained stable. A dark circular portion appeared in the center that the Colonel believed was spherical. The object appeared made of translucent, dirty gray material. The Colonel stated the object traveled at far greater speed than the bomber passing overhead at the time, made no noise, left no exhaust or trail, and simply disappeared from sight.

A check of airline records showed that a United Air Lines DC-4 was in the vicinity at 12:14 Pacific Daylight Saving Time, flying west-bound at 4,000 feet. However, one observer's description of a box-like object suggested it could have been a weather observation box used by weather observers. Additionally, a weather service memo noted that weather balloons were released one hour prior but ruled out due to adverse wind conditions.

The complete case file is reproduced below as held by the National Archives across 473 pages.