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The terrain is mountainous with steep slopes, The soils of the Allen Park Series, which formed on the mountain slopes between elevations of 6300 and 8200 feet, are loamy colluvium and weathered granite residuum. The surface layer, approximately 2 inches thick, is dark-gray, gravelly sandy loam. The subsurface layer is light brownish-gray, gravelly sandy loam. The Fern Cliff Series is loamy mixed alluvium on short fans and valley side slopes in the mountain area in the same elevation range. The top layer of this series is light-gray, stony sandy loam. The barren areas are predominantly exposed bedrock that consist of mixed materials, including granite, sandstone, shale, and lime- stone. The dominant land cover species is Ponderosa pine; above an elevation of 8000 feet, there are Some Douglas fir and lodgepole pines. , , .' ~ Little James Creek flows into town from the north, through mostly vacant land. Existing development ~n Jamestown is located on both sides of James Creek, from the confluence with Little James Creek at Ward Street to 13th Street. Land use is primarily residen- tial, single-family homes, with some business and commercial uses. 2.3 Principal Flood Problems Floods in the study area usually occur during the period of May through September. Mountain snowmelt in May and June contributes significant runoff, but serious flooding does not occur unless rainfall accompanies the snowmelt. Peak flooding will usually occur within a few hours after a single rainfall event. Flooding is generally of short duration, but may be prolonged significantly by snowmelt runoff. 6 The steep stream slopes create swift currents during a flood, which produce added damages. Debris carried by the fast-moving water not only threatens bridges and culverts, but batters houses and other structures on the flood plain. The bridge and culvert crossings often result in channel restriction, raising the water- surface elevation. Erosion undercuts and destroys structures which would otherwise receive little damage from inundation. Large quantities of rock are often deposited in portions of the channel, leaving little capacity for future floods. In June 1894, a floqd roared down James Creek and washed away much of the low-lying area of the town. The flood was caused by heavy rains accompanied by heavy spring runoff. Most of the houses on the north side of Main Street were ruined or washed away, as was much of the road. A similar flood occurred in August 1913, damaging or destroying almost every house along James Creek. All wagon and footbridges were destroyed, and it took two weeks to open the road to traffic. s J , ~ 4