. Compendium of meteorology. Meteorology. TREE GROWTH 109 TREES IN 24 AREAS Ml AJVA DOUGLAS fir â Ji 19 TREES IN 7 AREAS umeKemE k 1 f\ 8 TREES IN 4 AREAS A^ PINVON PINE ' 1850 I860 1870 1880 1890 1900 1910 1920 1930 1940 % 125 100 _75_ 129 ^100 â ^100 50 PONDEROSA AND ..q LIMBER PINES ^" -100 50 Fig. 3.âRegional tree-ring indices in the Colorado River Basin compared with gage data. Rainfall is expressed in per cent of the mean; tree growth in per cent of the mean trend; runoff in acre-feet X lO"". The runoff of the Colorado River pre- ceding 1895 is an approximation by E. C. La
. Compendium of meteorology. Meteorology. TREE GROWTH 109 TREES IN 24 AREAS Ml AJVA DOUGLAS fir â Ji 19 TREES IN 7 AREAS umeKemE k 1 f\ 8 TREES IN 4 AREAS A^ PINVON PINE ' 1850 I860 1870 1880 1890 1900 1910 1920 1930 1940 % 125 100 _75_ 129 ^100 â ^100 50 PONDEROSA AND ..q LIMBER PINES ^" -100 50 Fig. 3.âRegional tree-ring indices in the Colorado River Basin compared with gage data. Rainfall is expressed in per cent of the mean; tree growth in per cent of the mean trend; runoff in acre-feet X lO"". The runoff of the Colorado River pre- ceding 1895 is an approximation by E. C. LaRue ( Water-Supply Paper 395, 1916) on the basis of Salt Lake levels. {From University of Arizona Bulletin.) above Hoover (Boulder) Dam is seen (Fig. 3) to pro- vide a fair first approximation to the winter rainfall chronology of that region and to the river runoff. Independent 342-year indices for two types of pines mits a sensitivity to rainfall fluctuations which is at best on a much lower level than that of drought-site trees. The big-cone spruce of southern California has, how- ever, been found to show a sensitivity rivalling that of the best trees of the Colorado Plateau; a 560-year record has been constructed. Its value as an index of rainfall and runoff is indicated in Fig. 4. IS50 1660 1670 16801 1690 1900 1910 RAINFALL I SOUTH COAST RANGE I RUNOFF SAN GABRIEL RIVER (NEAR AZUSA) SPRUCE GROWTH SOUTH COAST RANGE Mm RAINFALL SOUTH SIERRA NEVADA. RUNOFF KINOS RIVER (AT PIEDRA) "^j" J L 1920 1930 1940 % 200 ^W^^v^^Vs^^ Fig. 4.âRegional tree-ring indices for southern California compared with gage data. Rainfall is expressed in per cent of the mean; tree growth in per cent of the mean trend; runoff in acre-feet X 10*. (From University of Arizona Bulletin.) The third regional survey of broad character, that of Keen [20] in the ponderosa pines of semiarid eastern Oregon, makes possible some centuries-long compari- sons with southern California and the Colo
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