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Figure 6. This oblique aerial view, looking upstream, shows the alluvial fan and terrace deposits at Soap Creek Rapids (Mile Ill. The river above the rapids is approximately 200 feet wide. The triangular alluvial fan ther back to the river or to the land areas well above the river, depend- ing upon the prevailing wind direc- tions. The lack of occasional high water has allowed many plants to become more firmly established and to ex- pand onto the remnant floodplain deposits. These recent invaders are densest on the steep, silty beaches and along wide, still-water stretch- es of the river where erosion is 393 American Scientist. Volume 62 deposited by Soap Creek enters from the left, constricting the channel and forming rapids. Severe erosion since Glen Canyon Dam has removed most of the shorefront sand and silt. The terrace deposits covering the fan have also been reworked by the wind into sparsely . vegetated dunes. (Photo by Alan Howard.) slowest. The most common of these plants is the tamarisk, an exotic shrub introduced from the Middle East to decorate the shores of Southwestern reservoirs (6). Al- though the tamarisk does help to hold some of the deposits in place, it often forms a veritable jungle along the river's banks. Other plants that have moved into re- duced stress zones are the cattail, brittle bush, Russian thistle, mes- quite, arrow weed, camel thorn, and sparse willow (Table 2). In ad- dition to the rapid development of new plant communities along the banks, the shallow-water areas of the river channel are becoming cov- ered with a thick green algal growth (Roy Johnson, pers. comm.), resulting from the reduced stress along the bed and the in- creased light penetration through the sediment-free waters. Murphy (7) has reported that the fis. / tic tio ! reg ~ l (sq ad: wa anI anI thE "ti, Th qUE em the cat 161 ere: too stre nel tari tim pos the (pre the and anc: flool Som mor dan: boui sane cern tine lem! Qua of t lossE BasE mad meal gap thr01 son ( phot son I by t] lishn conti chan and, year. Mal Colc Althc peopl nms the C ly, e'