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Cover page of Significant Changes to Twentieth-Century Temperature and Precipitation in the Sierra Nevada near Lake Tahoe: The Possible Anthropogenic Effect

Significant Changes to Twentieth-Century Temperature and Precipitation in the Sierra Nevada near Lake Tahoe: The Possible Anthropogenic Effect


A study of the weather records from six stations in the Sierra Nevada at and near Lake Tahoe, plus one station in the Diablo range of central California, reveals the following:

1. Since 1915, the date of the first major autumnal snowstorm has become progressively later at Tahoe City by 0.24 days/year (d/yr).

2. The change in the snowfall date results from an increase in the air temperature (T) at Tahoe City between 1909 and 2004, during the months of Septemberthrough December, of T′max = +0.011 °C/yr, T′min = +0.020 °C/yr, T′mean = +0.016 °C/yr. These values agree substantially with those published by Coats et al. (2006).

3. On average, the other five stations show a much smaller increase, amounting toT′max = +0.001 °C/yr, T′min = +0.012 °C/yr, T′mean = +0.007 °C/yr. Thismean value agrees well with the increase of T′mean = +0.007 – +0.008 °C/yr for the North American continent due to global warming (Jones and Moberg, 2003; Karoly et al., 2003).

4. The rate of temperature increase at Tahoe City is thus greater than would be expected from global warming and reflects a change in the microclimate of the Tahoe Basin, possibly due to human activity.

5. No overall change in precipitation with time is observed at any of the seven stations. However, statistically significant increases in precipitation with time occur, in the month of November, at the three Sierran stations located west of the Sierra crest, as well as at Tahoe City east of the crest. These increases coincide with the onset of the first substantial precipitation at these stations in the fall, and could be the result of “cloud seeding” by atmospheric pollutants, the precipitation becoming greater with time as the amount of pollution increases, and diminishing in December after these pollutants are washed out of the atmosphere by the first rains or snows.

Coats, R., J. Perez-Losada, G. Schladow, R. Richards, and C. Goldman: 2006, ‘The Warming of Lake Tahoe’. Climatic Change 76, 121–148.

Jones, P. D. and A. Moberg: 2003, ‘Hemispheric and Large-Scale Surface Air Temperature Variations: an Extensive Revision and an Update to 2001’. Journal of Climate 16, 206–223.

Karoly, D. J., K. Braganza, P. A. Stott, J. M. Arblaster, G. A. Meehl, A. J. Broccoli, and K. W. Dixon: 2003, ‘Detection of a Human Influence on North American Climate’. Science 302, 1200–1203.




Preface (Abstracts for Parts One and Two follow)

The two reports contained in this volume constitute a record of the writer’s studies from 1988–2008 of petroglyphs, pictographs and features at sites that appear to have been used by the Indians for astronomical observations. These sites are located:

(1) In the Providence Mountains in the Mojave Desert of southern California, discussed in Part One of this volume.

(2) On the Middle Fork of the American River in the Sierra Nevada of north-central California, discussed in Part Two.

The identification and study of sites used by the Indians for astronomical observations is of importance for two reasons. First, if we can identify the astronomical phenomena or events that were being observed, we may gain some insight into the astronomical knowledge of the users of the sites, and into their astronomically related ceremonies and practices. In some instances, we may also be able to establish the time periods in which the observations were made. Secondly, by studying the petroglyphs and/or pictographs associated with these sites, we may gain a greater understanding of the meanings of these symbols.

Studies of the petroglyphs and pictographs created by the Indians of the North American Continent began in the 18th and 19th centuries. These investigations were carried out by workers who had direct contact with Indians who still retained some knowledge of the meanings of these symbols, and still occasionally produced contemporary examples (Mallery 1893, and references therein; Martineau 1973, and references therein). It was the consensus of these workers that these symbols are not merely “art”, but are, in fact, a form of pictographic or ideographic writing, designed to convey a specific message to the proficient reader. During the 20th century, this concept was further developed by LaVan Martineau (1973), who used the techniques of cryptanalysis to demonstrate that the petroglyphs are not simply artistic designs, but are indeed the symbols of a written language. Unfortunately, there are as yet only a few “Rosetta Stones” for this language, so that to date it has only been possible to translate a relatively small number of these symbols (Martineau 1973).

The study of petroglyphs and pictographs at observing sites is thus of considerable importance. If, as noted above, we can identify the astronomical event or phenomenon that was being observed, we may then be able to deduce what the authors of the associated inscriptions were writing about. This, in turn, may then help both to confirm the translations that have been made of previously studied symbols, and to determine the meanings of additional ones.

Therefore, in the reports presented here some use has been made of Martineau’s (1973) findings on the structure and concepts of the pictographic language, and of some of the translations which he was able to make of particular symbols. Martineau’s work was based mainly on his studies of petroglyphs and pictographs in the Great Basin region. His findings are of particular relevance to the studies reported here since in both cases it is believed that the creators and users of the sites were peoples who shared a common ancestry with those of the Great Basin (Kroeber 1925:574–580; Gortner 1986:6–26). Thus, it is reasonable to expect that at least some of the symbols and language concepts used at the Middle Fork and Providence Mountains sites will be similar to those discussed by Martineau.

It should be noted, however, that the major conclusions of these two reports will remain essentially the same even if all reference to Martineau’s work is excluded.

Gortner, Willis A.

1986 The Martis Indians: Ancient Tribes of the Sierra Nevada. Portola Press: Woodside, CA.

Kroeber, Alfred L. 1925 Handbook of the Indians of California. Bureau of American Ethnology. Bulletin 78. Washington, D.C.: Government Printing Office. Mallery, Garrick

1893 Picture Writing of the American Indians. Annual Report of the Bureau of Ethnology 10:25-29. Smithsonian Institution: Washington, D.C.

Martineau, LaVan 1973 The Rocks Begin to Speak. K.C. Publications: Las Vegas.


Calendrical Observations in the Providence Mountains


Two sites in the Providence Mountains, located in the Mojave Desert of southern California, and their use for calendrical observations of the sun, have been described by Rafter (1985, 1987, 1991). These sites, CA–SBR–291 and CA–SBR–535, referred to by Rafter as Counsel Rocks and Shelter Rock, respectively, possess sunrise or sunset alignments as well as pictographs, petroglyphs and light-and-shadow events that indicate that they were used to determine the dates of the solstices, the equinoxes, and a mid-spring/summer event. The present paper discusses the results of further studies by the writer that provide support for Rafter’s interpretations, and which bring out additional details concerning the observations that were made at these two sites and at a third location nearby.

Rafter, John

1985 Archaeoastronomy of Counsel Rocks, A Ring of Pictured Stones. In Earth and Sky: Papers From The CSU-Northridge Conference On Archaeoastronomy, A. Benson, T. Hoskinson, and T. Conway, eds. pp. 109–122. Thousand Oaks, California: Slo’w Press.

1987 Shelter Rock of the Providence Mountains. In Rock Art Papers 5, K. Hedges, ed., pp. 25–32. San Diego Museum of Man Papers 23. San Diego: San Diego Museum of Man.

1991 More Sunlight/Petroglyph Interaction at Counsel Rocks. In Rock Art Papers 8, K. Hedges, ed., pp. 65–74. San Diego Museum of Man Papers 27. San Diego: San Diego Museum of Man.


Ancient Indian Astronomers on the Middle Fork of the American River


Two sites that appear to have been used for astronomically related observations are: FS 05–17–54–345 (CA–PLA–797) and FS 05–17–54–346 (CA–PLA–798). These sites were first recorded by W. A. Gortner (1988), who designated them MFM and MFN, respectively. For simplicity, they will be referred to by these Gortner designations throughout this paper. The two sites are located in the valley of the Middle Fork of the American River, in the vicinity of French Meadows; their locations are shown in Figure 1. They are situated on or near the tops of two outcrops of the dark, quartzite bedrock of this region that have been rounded and polished by glacial action. These outcrops rise some 37 m (120 ft) above the surrounding valley floor. This elevation places their tops above the fairly dense vegetation cover of the valley, and gives the observer on their summits a relatively unobstructed view of the surrounding skyline (ridgelines) in all directions.

Gortner, Willis A.

1988 The Willis Gortner Site Records, Volume 2: 19 Petroglyph Sites along the Middle Fork of the American River, Placer County California. California Department of Forestry and Fire Protection Office: Sacramento.