A NATIONAL PLAN FOR AMERICAN FORESTRY 439 



nonfprested valleys some, including the capital of the territory under 

 Mexican administration, were within the forest. There is little ques- 

 tion that the protecting vegetation near these settlements was partly 

 destroyed in the early nineteenth century. Destruction of vegetation 

 sufficient to menace watershed values, however, apparently did not 

 occur over extensive areas until sometime after the Civil War, follow- 

 ing introduction of large herds of cattle and sheep. Mining and 

 other settlement resulted in extensive fires and some devastation of 

 timber stands. 



Following deterioration of the grass and other protecting vegeta- 

 tion, rapid run-off of rainfall removed much of the surface soil over 

 enormous areas through sheet erosion, materially reducing the pro- 

 ductivity of the land. For example, an erosion survey of the drainage 

 above the Elephant Butte Dam made in 1931 by C. K. Cooperrider 

 and B. A. Hendricks of the Forest Service disclosed that 35 percent 

 of the area is being eroded seriously, 40 percent moderately, and the 

 remaining 25 percent slightly. While a much higher percentage of 

 nonf ores ted than of forested area was found to be seriously and 

 moderately eroded, the total forest area thus affected was large. 



The rapid run-off from these depleted and eroded lands has formed 

 an extensive system of gullies, small near the upper parts of slopes but 

 often 10 to 30 feet deep and several hundred feet wide in main stream 

 courses. Such a system of gullies is extremely efficient in concentrat- 

 ing water from torrential rainfall into flood proportions. The water 

 thus accumulated, heavily charged with soil and other debris, con- 

 tinually adds to its burden and its destructive power by erosion from 

 channel banks as it flows through the alluvial valleys. 



Floods and erosion combine to cause serious losses almost every 

 year. Excessive high water resulting from melting of snow, and from 

 torrential summer rains, cut away valley farm lands, wash out rail- 

 road and highway bridges, endanger lives, and silt up reservoirs, 

 other irrigation works, and stream channels. 



Kirk Bryan, on the basis of early records and of field surveys, has 

 outlined 72 as follows the trends on the Rio Puerco, in New Mexico. A 

 small channel existed before 1885. While the stream banks may have 

 been as high as 20 to 30 feet in places, in other places they were so 

 inconspicuous as not to be mentioned by early surveyors and explor- 

 ers. The river was subject to numerous floods of short duration and 

 to occasional floods of great magnitude which overflowed the valley 

 floor. Beginning in the late eighties, accelerated erosion has cut an 

 arroyo in some places nearly 50 feet deep from the mouth of the Rio 

 Puerco almost to its head. The present channel has an average depth 

 of 28 feet and an average width of 285 feet. The continuing erosion, 

 deepening and widening the channel, has destroyed much farm land 

 and caused the abandonment of six small settlements including Los 

 Cerros, San Ignacio, and San Francisco. Silt to the amount of 9,400 

 acre-feet a year, on the average, has been poured from the Rio Puerco 

 into the Rio Grande for the past 42 years. 



Because of floods the railroads and the State and county highway 

 organizations are forced to expend considerable sums for special road- 

 bed drainage and for protection works to prevent destruction of the 



Bryan, Kirk. Historic Evidence on Changes in the Channel of Rio Puerco, a Tributary of the Rio 

 Grande in New Mexico. Jour. Geology, v. 36, no. 3 : 265-282. 1928. 



168342 33 vol. 1 29 



