QUIROGA: a MEXICAN MUNICrPIO — BRANT) 



123 



crease in precipitation and decrease in temperatiu-e 

 frona the lake shore to the top of Tzirate. Since 

 mountains, hiOs, and slopes with a gradient 

 greater than 3 percent occupy the majority of the 

 area, there is rapid run-off, good drainage, con- 

 siderable soil creep, and much denudation and 

 erosion. Consequently, at present, over large 

 areas the soil cover is thin, and frequently the A 

 horizon has been stripped off completely. Most 

 of the soils are residual. Next in area are the 

 alluvial soils of the lake plain and the upland 

 depressions or joyas. At one time there were 

 extensive sheets of wind-deposited volcanic dust 

 and fine sand, but at present the older volcanic 

 "ashes" and sands (converted to tuffs and sand- 

 stones) are part of the basal complex underlying 

 the residual soils. The more recent "ashes" and 

 sands commonly are covered with thin veneers of 

 water-transported materials. Since March of 

 1943 there has been deposited a considerable 

 amount of "ash" from Paricutin. No one has 

 measured the thickness of the ashfall in the 

 Quiroga area, but judging from various local 

 accounts and the deposits noted on the vegetation 

 in the winters of 1944-45 and 1945-46 (before the 

 rains) it must have totaled quite a few millimeters. 

 Furthermore, many of the farmers around Quiroga 

 have remarked upon the increased fertility of the 

 soils since 1943. Colluvial soils have a spotted 

 minor distribution. 



Erosion has been very severe in the Patzcuaro 

 Basin. Many factors have contributed to this 

 process. There is a predominance of slopes and 

 steep gradients. The mature soils (as found on 

 some mesas, saddles, and gentle slopes) were 

 commonly deep and porous down to the imper- 

 meable tepetate (which will be defined later). 

 Most of the precipitation falls within a period of 

 120 days (June to October), and this commonly 

 comes in intense downpoiu-s of short duration 

 with accompanying high run-off. The natural 

 vegetation has been removed in large part. 

 Although the Tarascans had no grazing livestock 

 or plows before the Spanish Conquest, enormous 

 quantities of wood were cut for their perpetually 

 burning ceremonial fires. The well-developed 

 delta of the Aitoj'o del Sal to (as showTi on 16th 

 century maps) would indicate a long history of 

 erosion and sedimentation, as would also the 

 alluvial plains of the Llano de Santa Fe and the 

 Llano de Tzintzuntzan. The introduction of 



oxen, equines, sheep and goats in the 1520's and 

 1530's must have materially affected the natural 

 pasture and browse. European methods and 

 standards of construction and heating probably 

 increased the annual cut of pine, oak, and other 

 trees. The woodworking industries of Quiroga 

 {bateas, chests, desks, chahs, etc.) have been an 

 increasing drain on both softwoods and hardwoods. 

 The opening up of the national highway in the 

 past 10 years has increased the market for char- 

 coal. Despite remonstrances during all of the 

 nineteenth century and various laws since the 

 1880's, the pernicious custom of clearing by 

 burning (with the fires frequently getting out of 

 control) still obtains — as it probably has since 

 man first settled in the area. The excessive 

 deforestation in the general area was commented 

 on as early as the second half of the nineteenth 

 century (Romero 1860-63; Le6n, 1887-88). Also, 

 changes in population and in cultivation tech- 

 niques have accelerated erosion. 



Possibly the change from aboriginal "hole and 

 hUl" cultivation with a planting stick and hoe 

 to furrow cultivation with the iron-tipped wooden 

 plow drawn by oxen has been the most important 

 immediate agent in accelerating erosion. With 

 the plow and its furrows came the first widescale 

 breaking of a probably nearly continuous plant 

 cover. Concomitant was the demand by Euro- 

 peans and their livestock for wheat, barley, and 

 other cereals and hays. Since the areas devoted 

 to maize could not be reduced much, if at all, this 

 demand forced an expansion of tillage into the 

 marginal hitherto little cultivated steeper slopes. 

 The fm-rows probably ran with and across the 

 slope at the whim of the cultivator, as is still true. 

 This was not too bad if a crop was growing during 

 the rainy season. But from 1810 until recently, 

 rebellion, war and brigandage caused numerous 

 periods of abandonment of all fields at any 

 distance from the towns and villages. In the 

 Quiroga area the general periods 1856-76 and 

 1916-26 saw the most abandonment of fields. 



It is virtually impossible to date the initiation 

 of even the largest eroded areas, such as the slopes 

 inamediately^to the north and east of Quiroga. 

 Among the older inhabitants one can obtain state- 

 ments varying ^from "The erosion began during 

 the Revolution" (some 30 years ago), through 

 "It was as bad>t the turn of the century as it is 

 now" (some j^50^ years ago), to "It was already 



835847—50 



