CYCLES 



121 



as also 8.5 and 17 year cycles. Further discussion will be found below 

 under Solar Records in Tree-Growth, page 125. 



Pike's Peak area mean curve — The groups in the Rocky Mountain 

 zone cover a smaller area than those in the other zones. Thus the 

 area represented by the mean curve is limited to the east slopes of 

 Pike's Peak in the vicinity of the Cog Railroad. The homogeneous 



1700 



80 



a 0.5 



~ 1300 10 20 30 40 1850 60 70 80 90 1900 10 1920 



YEARS 



Fig. 13 — Pike's Peak area mean curve, PPM ; average of six groups, standardized 



and smoothed 



collection of groups includes six, PPB, HNT, LNT, C, ST, and BDF. 

 The Laramie group and those from Santa Fe and the Aztec region are 

 similar, but not quite enough like the central collection to be included. 

 The mean curve of the six named is shown in figure 13. It appears to 

 show strongly a 5, 10, 20 year cycle and a triple sunspot cycle divided 

 into halves and quarters (that is, an 8, 17, 34 year cycle). 



Sierra Nevada mean curve — The distribution of groups in this 

 zone is better than in the other zones. From The Dalles in northern 



1700 10 20 30 40 1750 60 70 80 90 1800 



a 

 a 

 < 



I8C0 10 20 30 40 1950 60 70 80 90 1900 10 20 1930 



Fig. 14 — Sierra Nevada area mean curve, SNM ; average of four groups, standardized 



and smoothed 



Oregon to Pine Valley near San Diego the nine locations are fairly 

 well spaced. There is pronounced similarity in the smoothed curves 

 in all of these except Klamath Falls and Pine Valley, but the best 

 agreement occurs between those in the Sierra Nevada Mountains from 

 Calaveras to Mount Wilson and the mean curve is the average of 

 these, namely, CVP, BC, EP, and W groups. It is given in figure 14. 



