72 CLIMATIC CYCLES AND TREE-GROWTH 



little above that of Flagstaff and is about the same as that of the Fort 

 Valley group, with which the curve, therefore, can be compared for the 

 shadow effect. Mr. Hawkins measured these specimens by the long- 

 plot method and, without standardizing, plotted a curve from the 

 averages. This curve, 1717 to 1923, was Hanned mathematically and 

 the cycle plot was made by him also. This smoothed curve from 1750 

 on is shown in figure 4. The great variation between maxima and 

 minima is at once apparent and is characteristic of lower and drier 

 altitudes. The shadow effect does not appear to differ much from 

 simple reduction in rainfall, equaling in this case the effect of about 

 1,500 feet change of altitude. The spacing of the maxima is strongly 

 of the Flagstaff or Arizona type. The observed cycles are 14.1 (3), 

 19.4 (2), 27.3 (2, -J) and 40 (2, oc. £). 



FLAGSTAFF NORTHEAST GROUP (NE) 

 This group was collected on June 14, 1923, in connection with 

 prehistoric dating problems, to determine with certainty whether the 

 part of the Flagstaff forest area nearest the prehistoric ruins carries 

 the same ring records as the very old trees just south of town. Dr. 

 E. S. Miller, of Flagstaff, was kind enough to take me out 19 miles on 

 the Tuba road and there, at the edge of the forest, I took four incre- 

 ment-borings. Mr. Hawkins measured these in 1923 by the auto-plot 

 method. These were thoroughly rechecked by the writer (as in all 

 cases). These individuals were so nearly alike in average growth that 

 they needed no further standardizing. The curve, 1678 to 1922, 

 identifies exactly with the Flagstaff record. It was smoothed by 

 graphic Hann by Mr. Austin and the part from 1750 on is shown in 

 figure 4. The cycle plot analyzes as follows: 8.5, 11.6 (2), 14.3 (2, 

 oc. £), 19.4 (2), 27.7 and 36 (2); these classify as Arizona type, though 

 the 11.6 is not so common as on the coast. 



GRAND CANYON GROUP (GC) 

 The edge of the Grand Canyon is 65 miles north and a little west 

 of Flagstaff. Leaving the San Francisco Peaks and traveling north, 

 one descends gradually for a time away from the pines, down through 

 the cedars, across a barren area, then up gradually through the cedars 

 and into the pines which border the canyon. Much of the forest area 

 near the canyon is perfectly flat. The Grand Canyon group was taken 

 in early July 1920, at points scattered several miles along the south 

 rim from a little west of Grand View to the Buggeln property, which 

 used to be Tolfree's Hotel, at the top of the old historic Hance Trail, 

 a distance of 5 or 6 miles. The soil here is a thin layer of earth over 

 limestone. There appears to be very little surface drainage and it is 

 probable that the water soaks down through the limestone formation 

 and emerges in springs in the canyon. In the early days, Tolfree 's got 

 its drinking-water from artificial "tanks" or pools of standing water 



