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natural setting, and in exhibiting their mutual relationships. It. fits 
one the better to understand the reports of investigations of special 
aspects or particular features of the territory observed, But its value 
is greatly enhanced if it leads to the recognition of problems for future 
research. And this particular excursion impressed me as especially 
valuable in that regard. 
The territory which we had under observation has been rather 
neglected by geological investigators. Excellent work has been done, 
but only in comparatively small amount. There has been an impres. 
sion that the problems were not especially inviting, that the features 
were of comparatively few types and somewhat monotonous. But in 
reality it appears to be rich in problems of most interesting types. 
The physiographie history—the history of the development of the 
present geography—offers a most excellent field for investigation. The 
comparative uniformity of rock material over large areas has to a large 
extent freed the action of erosive agencies from the complications of the 
differential resistance of a multiplicity of roek types. The methods 
would necessarily be largely physiographic but not exclusively so. The 
remnants of Tertiary lavas and sediments resting on the old erosion 
surface of the mountain belt are apparently few in number, but offer 
possibilities for the discovery of evidence of important events in the 
history of the region, for correlating the events of the highlands with 
those of the lowlands, and the more accurate dating of the movements 
that raised the mountains above the coastal and desert belts. 
Ridges rising above the general summit level with suggestive out- 
lines seem to indicate internal movements in the mountain block that 
call for elucidation. 
Peculiar drainage features such as are presented by the valleys 
about Tecate Mountain, point to events that illustrate general condi- 
tions in the physiographic history. And peculiar stream valley align- 
ments, such as the long and straight armed cross formed by Pine, Lyons 
and Cottonwood creek valleys, call attention to structural features that 
are not otherwise apparent on a rapid trip through the field. 
The nature of the transition zones between mountain belt and the 
lowland belts is still imperfectly understood. The structure, strati- 
graphy, and physiographie history of the lowland belts are only known 
in a general way. 
Careful studies of the sediments in the east and west. basins would 
undoubtedly yield facts important for the history of the basins, and 
also contribute to an understanding of the character and history of 
the adjoining mountain belt. 
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