FOREWORD BY DR. WALTER E. LAMMERTS In my article "Trees Indicate Recent Origin of Yosemite Valley"’ brief reference was made to the explanation, by J. D. Whitney, a former California State Geologist, of how Yosemite Valley was formed. After showing why this beautiful valley could not have been formed by erosion, he suggested that the entire floor of the valley had suddenly subsided. Josiah Dwight Whitney lived from 1819 until 1896, and was state geologist from 1865 until 1882. He wrote a number of important books, including: "Metallic Wealth of the United States" (1854); "Mountain Heights in the United States" (1862); "The Yosemite Book", a beautifully illustrated rare book, (1868); and the more practical "The Yosemite Guide Book" (1874). The following is an excerpt from The Yosemite Guide Book, pages 114-l 22. Besides giving Whitney’s opinion as to how the valley was formed, it is most interesting because of the evidence given for the recency of the erosion of the Sierra Nevada mountain chain. The Table Mountain lava on each side of the Stanislaus River at Abbey’s Ferry was of recent origin, as is shown by fossils under the volcanic mass. Yet the Stanislaus canyon is over 2,000 feet deep. Whitney’s opinion that John Muir was wrong in thinking that the valley was formed by erosion by ice, whereas in fact there is no proof that glaciers ever occupied the valley, is also very interesting. Maybe our Research Committee could encourage further investigation of this matter.