TREE RECORDS: GEOGRAPHICAL DISTRIBUTION 77 



THE ROCKY MOUNTAIN ZONE 



YELLOWSTONE GROUP (Y) 



This group of five increment-cores of white-barked pine (Pinus 

 albicaulis) was collected on August 20, 1920, at the eastern edge of the 

 flat top of Specimen Ridge, west of and opposite the buffalo farm, in 

 northeast Yellowstone Park. The trip was made from Camp Roose- 

 velt with the assistance of Mr. A. G. Whitney. The specimens were 

 cross-identified and dated in 1926. They were measured by Mr. 

 Austin, using the long-plot method. They were standardized and 

 give a record from 1693 to 1919. The curve from 1750, smoothed as 

 usual, and shown herewith in figure 5, does not closely resemble the 

 other Rocky Mountains curves, though its cycles are distinctly of that 

 type. They are 8.5 (3), 10.4, 12.5, 17.1 (3, oc. J), 25.6, 30.3 (oc. £). 

 Here we see the 17-year period which is characteristic of this eastern 

 zone. 



LARAMIE. WYOMING, GROUP (LW) 



This group of four cores, of which three only could be dated, was 

 collected on June 11, 1925, while motoring from Fort Collins, Colorado, 

 to Laramie, Wyoming. At some point not far from the State border 

 the road passes through a slight ravine with pine trees on the steep 

 slopes. The three cores afterwards used were obtained here. A few 

 miles farther on, a very large pine growing in a bleak flat area was 

 bored, but the outer rings were too small for certain dating. These 

 specimens were measured by Mr. Austin, using the long-plot method. 

 The records were each standardized and the curve, 1754 to 1924, was 

 smoothed by graphic Hann, which is shown in figure 5. Though its 

 variations are immense, it closely resembles the typical Pike's Peak 

 curve. Its cycles present the characteristic 17-year period with what 

 are probably some of its variants. The cycles are: 6.3 (2), 8.2 (3), 

 11.5 (oc. i), 15.9 (oc. £), 17.4, 18.2, 19.1 (oc. $), 25.0 (oc. J), and 

 35 (2). 



CLEMENTS'S PIKE'S PEAK GROUP (C) 



In 1919, Dr. F. E. Clements initiated this study of the Rocky 

 Mountain zone by sending me nine sections of trees from the vicinity 

 of the Alpine Laboratory, which is just south of the Cog Railroad 

 above Manitou, at an elevation of 8,700 feet. He described the 

 location of these trees as follows: Three yellow pines from north of 

 track with a south exposure, three Douglas firs from above cabins 

 with a northerly exposure, and three Engelmann spruce from near the 

 brook, with a northeasterly exposure. These were actually cut and 

 packed by Mr. C. W. Cherry, who later helped me at Tucson for a few 

 months. One of the pines was defective and could not be used, and 

 the remaining eight trees were averaged and plotted in a curve from 

 1783 to 1919. This was recently Hanned graphically, as shown in 



