By Edwin D. McKee, Park Naturalist.

IN A PREVIOUS ISSUE of Nature Notes, (vol. 4, no. 5), the writer pointed out the difficulties and the several uncertainties involved in determining the age of the Grand Canyon. He showed that, based on the radio-active method of calculating and on Capt. C. E. Dutton's (1) theory of origin, the age may be roughly placed between seven and nine million years.

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(1) Dutton, C. D., "Tertiary History of the Grand Canyon District". U.S. Geol. Survey Mon. 2, pages 77, 221.

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It seems only fair to point out, therefore, that there are other theories of origin of the Grand Canyon and that according to those held by Dr. H. H. Robinson and by Dr. Eliot Blackwelder, its origin has been since the beginning of Pleistocene time, or less than a million years ago.

The conclusions of Dr. Robinson (2) concerning the origin of the Grand Canyon are based on a reconstruction of the major events in the region and on a study of the sequence of periods of folding, faulting and erosion. He sums up the history of the region since the start of the Colorado River in the following way:

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(2) Robinson, H.H., "A New Erosion Cycle in the Grand Canyon District, Arizona". Jour. Geology, vol. 18, no. 8, (Nov.-Dec. 1910) pp. 763 ff.

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1. First part of Quaternary - Land stood at no great height above the sea.

2. Middle or latter part of Quaternary - Region raised from 4,000 to 6,000 feet.

3. Latter part of Quaternary - Canyon cycle of erosion marked by the development of a canyon system of drainage of extreme youthfulness.

Dr. Blackwelder (3) considers that the Colorado River has had its origin since the beginning of the Pleistocene Period because the Tertiary deposits along its lower course are local - of the types made by short streams in interior basins and because they show no evidence of a large river.

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(3) Blackwelder, Eliot, "Physiographic History of the Colorado River", Abstract G.S.A. 1931.

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In accordance with the theory of a comparatively recent origin of the Grand Canyon (less than one million years) is the narrowness of its gorge. A great river whose valley has an average width of only ten miles and a maximum of eighteen, is certainly in a youthful state of development.