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18 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
fork and Hobble creek at the two ends of the Spanish peak mass were 
mentioned (p. 146) as more maturely opened than certain other valleys 
of the Wasatch, farther north. A closer examination of the side 
slopes of these cross valleys showed them, however, to be in no essen- 
tial respect unlike the side slopes of the ravines that have been carved 
in the west face of the mountain mass between them, although the 
cross valleys are more conspicuous because they are cut down so deep 
and are continuous through the range. The valleys here are wider 
open and their slopes are better graded than is the case with the can- 
yons of the Provo Wasatch, next farther north, because the lime- 
stones there are more resistant to arid weathering than are the arena- 
ceous beds of the Spanish peak mass. We had good opportunity to 
note these features during the morning ascent and again in the after- 
noon descent when we returned to the western base of the mountain 
by way of the canyon of Spanish fork. It is worth mentioning that 
the spurs which descend into the cross valleys have terminal facets, 
like those which terminate the spurs at the western base of the range. 
This is evidently because the cutting action of the streams in the cross 
valleys replaces the cutting action of the fault on the range front. 
While making the descent we had a good sight of the high-level 
Bonneville terraces in Diamond creek valley, a northern branch of 
Spanish fork several miles back in the mountains. The terraces were 
distinctly of stream origin, as there was a strong down-valley slope on 
their upper surface which originally led down to the Bonneville level 
at the delta margin. We were thus better prepared than before to 
appreciate Gilbert’s explanation of the smaller size of the ancient 
deltas at the high Bonneville level than at the lower Provo level: for 
during the stand of the ancient lake at the Bonneville level all the deeper 
valleys that were flooded far back into the mountains had to be ag- 
graded, and so much material was needed for this purpose that the 
surplus for forward delta growth in the main body of the lake was 
small; but when the lake fell to the Provo level, the waste accumu- 
lated in the valleys was easily and promptly devoted to delta building 
in the lake itself; and hence the Provo deltas rapidly grew to large 
size. 
Our camp for the night of July 13 was at an isolated ranch about 
two miles northwest of the mouth of Spanish fork canyon, and was 
notable for the strength of the mountain breeze that began early in the 
evening and blew with increasing strength all night and after sunrise 
the next morning. Everything movable was drifted away, and two of 
the party had a quarter-of-a-mile search down the wind for their hats. 
