108 CLIMATIC CYCLES AND TREE-GROWTH 



of 7,300 feet, at the southwest base of the mountain, and Flagstaff 

 High group, at 9,000 feet, directly up that same southwestern slope. 

 The first effect of altitude is an increase of mean ring-size from 1.10 

 mm. to 1.95 mm. resulting without doubt from the increase of pre- 

 cipitation at the higher point. The rings themselves of the higher 

 group appear far more complacent, but can be dated in terms of the 

 Flagstaff series. In comparing the smoothed curves of the two groups, 

 the variations (those which become conspicuous in the cycle plots) 

 decrease from 34 per cent at Fort Valley to 25 per cent in the upper 

 location, and at the higher point lose much of their resemblance to the 

 other smoothed curves of that region. On comparing the cycles one 

 finds at the upper station the 17.3-year length, which is very rare in 

 the Arizona area. It is more common in the Rockies and on the 

 northern coast. 



Shadow — As previously explained, mountain shadow is an expres- 

 sion which here refers to the side of the mountain away from the 

 direction from which storms usually approach. It is, of course, on 

 the east side of the San Francisco Peaks, since the winter storms come 

 from the west and southwest. Two groups were taken to the east 

 and northeast of the peaks; the shadow group (SH) close in at the 

 foot of the steep eastern slopes at about the same level as Fort Valley, 

 and Flagstaff Northeast group (NE), about 7 miles farther out from 

 the mountain center and at the edge of the pines at an elevation some 

 500 feet lower. The ring-sizes in the SH group is 1.52 mm. and in the 

 NE group 1.17 mm. The cycle variations of the former are about the 

 same as FV (34 per cent), but the corresponding variations of NE are 

 near 70 per cent. On examining the smoothed curves each seems to 

 be free from short interfering cycles, and perhaps this is its special 

 quality. The difference between them appears to be a question of 

 water-supply, which is abundant very close to the mountain, but 

 rapidly decreases to the east. This same characteristic of relative free- 

 dom from short-period cycles appears in the Lower Rim and the 

 Cibecue groups and in the Charleston Mountain group. 



Soil and bed-rock — Many of the Flagstaff groups grew on soil that 

 was not distinctive. The first, for instance, was on deep soil formed 

 by an outwash fan from Woody Mountain, which is igneous rock. 

 The 500-year trees of FLU grew on a considerable soil over lime- 

 stone. Probably the old group at Lake Mary, whose curve is given 

 in Volume I, page 26, illustrates best the effect of this limestone 

 soil. Its mean ring-size is about 0.75 mm. It shows rather stronger 

 variations than the FL curve. For comparison, a group of two trees 

 at the Lava Beds, 15 miles northeast of town, may be quoted. These 

 trees were about 350 years old and show large growth when the trees 

 were small and then a very long continuance of uniform small growth 

 (0.50 mm. in one and 0.75 in the other), with slight variation. Lava 



