DATA AND UNDERSTANDING 119 
This investigation led to results which added something to our 
knowledge of interrelations of sediment and hydraulic factors in 
ephemeral channels (7). It emphasized an unexpected similarity 
between perennial channels in humid areas and the ephemeral 
channels of semi-arid areas. Certain differences, however, were 
demonstrated, particularly in sediment load characteristics. These 
differences appear to be reflected in hydraulic factors, particularly 
in flow velocity. 
The current problems of sediment deposition, of arroyo cutting, 
land management, and water supply emphasize a present de- 
ficiency in our understanding of basic physical mechanisms in 
this environment. Basic data are necessary for, but do not substi- 
tute for, basic research. 
We have not extracted all the knowledge it is possible to gain 
even from records and data already collected. Rainfall measure- 
ments must be interpreted with an eye to topography, vegetation, 
and land use. The arroyo problem presents so complex an interre- 
lation between soils, geology, vegetation, hydraulics, and history, 
that no single discipline can take precedence over others if under- 
standing is to be achieved. These are only two examples of 
unsolved problems. 
If we are to achieve understanding and not merely content our- 
selves with the collection of facts, we must bring to the task the 
zeal implied by the words on Inscription Rock, “A su costa.”’ 
REFERENCES 
1. Bryan, Kirk. 1925. Date of channel trenching (arroyo cutting) in 
the arid Southwest: Science 42, 338-44. 
2. Hack, J. T. 1942. The changing physical environment of the Hopi 
Indians. Peabody Mus. Nat. Hist. Papers 35, 3-85. 
3. Judson, S. 1953. Geology of the San Jon site, eastern New Mexico 
Smithsonian Misc. Coll. 121, 1. 
4. Leopold, Luna B. 1951., Rainfall frequency: an aspect of climatic 
variation. Trans. Am. Geophys. Union 32, 347-57. 
§. Leopold, Luna B., 1951, Vegetation of Southwestern watersheds in 
the nineteenth century. Geog. Rev. 41, 295-316. 
6. Leopold, Luna B., and J. P. Miller. 1954. A post glacial chronology 
for some alluvial valleys in Wyoming. U. S. Geol. Survey Water 
Supply Paper 1110-A. 
