See biography by W. M. Davis in the Memoirs of the National Academy of Sciences, Vol. XXI (1926).
Gilbert published a study of the former ancient Lake Bonneville in 1890 (the lake existed during the Pleistocene), of which the Great Salt Lake is a remnant. He named that lake after the army captain Benjamin L.E. de Bonneville, who had explored this region previously.
In 1891 in one of the most controversial moves of his career, he proclaimed that Coon Butte in Arizona was the result of a volcanic steam explosion rather than an impact of a meteorite. Gilbert had based his conclusions on a belief that if it was an impact crater then the volume of the crater including the meteorite should be more than the ejected material on the rim and also a belief that if it was a meteorite then iron should create magnetic anomalies. Gilbert's calculations showed that the volume of the crater and the debris on the rim were roughly equal. Further there were no magnetic anomalies. Gilbert argued that the meteorite fragments found on the rim were just "coincidence." Gilbert would publicize these conclusions in a series of lectures in 1895. Subsequent investigations would reveal that it was in fact a meteor crater. Ironically, Gilbert would be among the first to say that the moon's craters were caused by meteors rather than volcanos.
He joined the Harriman Alaska Expedition in 1899.
Gilbert is considered one of the giants of the sub-discipline of geomorphology, having contributed to the understanding of landscape evolution, erosion, river incision and sedimentation. Gilbert was a planetary science pioneer, correctly identifying lunar craters as caused by impacts, and carrying out early impact-cratering experiments. Gilbert was one of the more influential early American geologists.