EROSION AND, DEPOSITION IN THE SOUTHERN 
ARIZONA BOLSON REGION 
(C5618, AONE AUNT 
The University of Arizona, Tucson, Ariz. 
OUTLINE OF PAPER 
INTRODUCTION 
PHYSIOGRAPHIC DIVISION OF ARIZONA INTO PLATEAU AND BOLSON COUNTRY 
DISCUSSION OF THE TERM “‘ BoLSoN ”’ 
TOPOGRAPHICAL FEATURES OF THE BOLSON 
Rock surface 
Bajada 
Playa 
ANALYSIS OF GEOLOGICAL AGENCIES UNDER THE STIMULUS OF ARIDITY 
Torrential precipitation 
Theoretical analysis 
Description of bajada building 
Factors affecting slope of bajada 
Wind action 
Method of attack 
The development of resistant pavements 
Underground water 
Water level 
Moisture table 
Crust deposits 
Cumate. Discussion of the factors quantitatively important, and classi- 
fication of the following types 
Type 1. Torrential precipitation dominant 
Torrential concentration (extreme or moderate) in either case with daily 
temperature difference (extreme or large) 
Type 2. Protective plant covering controls 
A moderate and distributed rainfall, with no great extreme of daily 
thermal range 
Type 3. Wind action important 
A thin distributed rainfall grading to no rainfall, and daily temperature 
difference (extreme or large) 
DEPOSITS OF THE BOLSON 
The bajada outwash. (a) Inclination. (6) Upper limit. (¢) Size of 
material. (d) Shape of boulders. (e) Decomposition of material. 
(f) Sorting. (g) Arroyo trains. (#) Sand pockets. (z) Change in 
layers. (7) Stratification. 
Playa deposits. (1) Lake. (2) Standing water mud sheet. (3) Outwash 
mud sheet. Modifications induced by evaporation and wind erosion. 
Structure of the lake deposits. (@) Strands and terraces. (6) Dis- 
tribution of coarse and fine. (¢) Composition and lack of subaerial 
markings. 
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