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drainage area of the Florida at its confluence point with the Animas River is approximately 221 sq m!. The La Pllta River OJiginates in the La Plata Mountains in the western portion of the county. It generally flows from north to south following the alignment of State Road 140 from its he"dwaters area south into New Mexico. The La Plata River is the largest stream system within the county for which no floodplain information (either detailed or approximate) has been developed. At the Colorado..New Mexico state line,:he drainage area to the La Plata is approximately 331 sq mi. La Plata County is primarily a rural community with the ;:mly significant urbanization being the Durango area. Landuse within the major river basins of the county consists mainly of undeveloped mountain areas and agricultural uses in vallel' and lower elevation areas. FI~'odinl! Problems and Floodinl! Historv G(,nerally, severe floods on the major streams of La Plata County such as the Pine, Florida, Animas and La Plata Rivers are the result of general storms occurring between July and October. G(:neral storms are characterized by prolonged, heavy rainfall over a large area and result in peak flows of moderate volume and duration. High..intensity, short duration cloudburst-type rainstorm", which are typical during the summer months, cause flooding only on streams with smaller drainage areas. Flooding potential on the larger streams though, also exists from the rapid melting of snow in the late spring. Snowmelt flood flows are characteriz(,d by moderate pe"ks, lar:~e volumes and long durations. Snowmelt flc'ods are generally less damaging than those resulting from general rainstoffils. Flooding information for La Plata County prior to the turn of the century is practically non- existent. On the Animas River, large floods are known to have occurred in 1896, 1909, 1911, 1927,1937,1941,1946,1949,1970 and 1972. The largest of these events occurred on October 5, .1911. During that storm, a peak discharge of 25,000 ds was recorded on the Animas River. Thi.s is the worst flood event on record for the entire San Juan River Basin and major flooding also occurred in other river valleys. Major snowmelt floods occurred on the Animas River in June 1927, May 1941 and June 1949. Th(, flood of June 1927 was the result of rainfall on melting snow and produced a peak flow of approximately :20,000 cfs. On the Los Pinos River major flooding occu:rred in Jl911, ]927, Jl957 and .1970. In 1957, VaUecito Reservoir was filled to capacity and floodgates were opened releasing approximately 13,000 cfs. In 1970, a thunderstorm event produced approximately 4.:5 inches of rain within a 6- to 12-hou:: time period and a number of vehicles and homes above Vallecito Reservoir were damaged. Pr!~vious Studies The OIiginal PIS for unincorporated La Plata County is dated December 15, 1981. The 1995 revision of the FlS was carried out to incorporate intermittent channelization of the Animas River in the vicinity of the James Ranch property and more detailed topography obtained for this reach. The revised re"ch of the Animas River was Oliginally studied in .198] using detailed methods and 1995 3