Show historical sketch of morgan count county y continued from last week the walls of the valley bear terraces at several levels and the study of these cannot fall fail to throw light on the valleys later history but such scattered observations as I 1 have been able to make have opened more questions than they nave have answered at about 1000 feet above the bonneville plain Is a grade plain now dissected that truncates the inclined pliocene strata it was most clearly seen at the north end of the valley and probably corres ponds to the upper of two andl s terraces east cast of the north end less definite high terraces appear farther south on the east sine and in round valley the fact that corresponding correspond ng terraces were not discovered on the west side of the valley suggests the possibility of an extensive late pliocene deformation or dislocation that involved the adjacent part of the wasatch range the principal part of the alluvial alluvia i i floor of the valley was laid during the provo stage of lake bonnevalle Bonne viTle at that time a large delta wa was s b built r u ailt by weber river against the west face of the wasatch range and the floor of the valley was graded in relation to the delta as a base level the material was brought not only by the river but by many of lis irs local tributaries tributa ries and a large contribution was furnished by east canyon creek which traverses the south end of the valley beyond ane point at which the river enters at the earlier and higher stage of the pleistocene lake the valley contain ed a bay the shore lines of which are readily recognized at a number of points since the fall of the lake waters from the provo level the weber and some of its tributaries tributa ries have bentren entrenched ched themselves in the provo plain but the amount of erosion has been small the depth of the incised channels Is greatest at the outlet of the valley and diminishes upstream until it ceases to ue at morgan where the weber enters the valley east canyon creek still hows flows at the level of the plain it built in the pro ni bench a U S geological survey studies of basin range structure by karl kari gilbert professional paper united states government printing office washington 1928 continued in next weeks news |