ROCK-CUT SURFACES IN THE DESERT RANGES 449 
provided the plane surface now scarred by recent dissection be 
assumed restored. Post-Quaternary faulting (probably an effect 
of more widespread uplift than is indicated by relative movements 
of blocks) is a sufficient cause for the dissection which has occurred. 
A hypothesis to explain the features described above may now 
be presented. ‘The intention is not to follow a process throughout 
all its possible variations, but to suggest an idea which may serve 
as a nucleus for future elaboration. All the processes by which 
rock-cut benches may be formed need not be enumerated. The 
facts in this case point obviously to the encroachment of an accu- 
mulating gravel sheet upon a highland area. The end result now 
achieved may perhaps be attained as follows. 
An area (of which the Basin Range system is an example) may 
be so warped by regional uplift that inclosed basins are formed. A 
climate is postulated of such aridity that permanent lakes will not 
rise to such altitudes as to overflow the rims of the inclosed basins. 
Such basins are favorable for the rapid sub-aerial accumulation of 
detrital matter. 
Active erosion within this system now becomes regulated by 
an all important factor: progressive burial by alluviation of low-lying 
areas. It is conceived that a central portion retains its original 
topographic sculpture because of complete oversweep of débris. 
Each succeeding portion of topography before it is buried will have 
been more reduced, will have been more softened in that it has 
suffered a longer period of exposure than the portion immediately 
preceding it. 
The rising edge of the gravel sheet acts as an effective control below 
which erosion cannot take place. The result is unavoidable if the 
time factor and the factor of area are sufficiently large. A process 
tending toward leveling with respect to the gravel sheet will proceed. 
But the gravel sheet has been gradually rising; therefore, the lev- 
eled surface is a sloping plain thinly veneered with gravel. 
A second process, it is believed, plays an important part in this 
result. The feature which leads to the recognition of the process 
is the abrupt change of gradient at the mountainward border of the 
rock-cut plain. A consideration of the character of the stream 
channels which debouch upon the rock-cut plain may give a clue 
