28 ' THE SERI INDIANS [eth.axs.17 



of the water: the product of the semiannual storms suffices to form a 

 meager supply of ground water, which is diffused in the sands and 

 softer rocks of the plains, and concentrated in the narrow channels 

 carved through the dense granites of the sierras; and enough of the 

 flow passes the barriers to supply deep wells in the terminal fan, as at 

 the frontier ranches Libertad (abandoned) and Santa Ana, just as the 

 subterranean seepage from the ISonora more richly supplies the deep 

 well at San Francisco de Costa Rica. In these lower reaches the min- 

 eral salts, normally jiresent in minute quantities, are concentrated so 

 that the water from these wells is slightly saline, while deeper in the 

 desert the scanty water is quite salt. 



In Seriland i)roper the distribution of potable water is conditioned 

 by the meager precipitation, the local configuration (shaped largely by 

 sheettiood erosion), and the disturbance of equilibrium of the scanty 

 groundwater due to the tilting of the province. The most abundant 

 permauent supply of fresh water is that of Arroyo Carrizal, which is 

 fed by drainage and seepage from the broad and lofty mass of pervious 

 rocks forming the southern part of Sierra Kunkaak, the abundant 

 supply being due to the fact that the eastern tributaries are energetic- 

 ally retrogressing into the mass in deej) gorges which effectually tap 

 the water stored during the semiannual storms. The arroyo and valley 

 of Agna Dulce are less favorably conditioned byreason of atrend against 

 the tilting of the province and by reason of the narrower and lower 

 mass of tributary rock in the northern part of the range, and the flow 

 is impermanent, as indicated by the absence of canes and other stream 

 plants; yet four explorers ( Ugarte, 1721 ; Hardy, 1S2G; Espence, 1844; 

 Dewey, 1875) reported fresh water, apparently in a shallow well tapping 

 the underflow, at the embouciiure of the arroyo. On the eastern slope 

 of Sierra Kunkaak there are several arroyos which carry water for weeks 

 or even mouths after the winter rains, and sometimes after those of 

 summer; but the only permanent water — Tinaja Anita — is at the base 

 of a stupendous clitt' of exceptionally pervious and easily eroded rocks, 

 so deeply cut that ground- water is effectually tapped, while an adjacent 

 chasm — Arroyo Millaid — is so situated that the clitt'-faced spur of the 

 sierra above the tinaja absorbs an exceptional proportion of the surface 

 flowage from the main crest. The tinaja (figure 3) is permauent, as 

 indicated by a cauebrake some 20 by 50 feet in extent, and by a native 

 fig and a few other trees — though the dry-season water-supply ranges 

 from mere moisture of the rocks to a few gallons caught in rock basins 

 within the first 50 yards of the head of the arroyo. No other ])erma- 

 nent supplies of fresh water are known on the island, though there are 

 a few rather persistent tinajjas along the western base of Sierra Manor 

 above Willard point. 



On the mainland tract there is a clitf-bound basin, much like that of 

 Tinaja Anita, at the head of Arroyo Mitchell and base of Johnson peak, 

 christened Tinaja Trinchera; but the range is narrow and the rocks 



