WATER RESOURCES OF ORANGE COUNTY 9
in the eastern part of the county is a part of Puri and Vernon's (1964, figure 6) Eastern Valley. The low area east of Rock Springs is a part of the Wekiva Plain and the Econlockhatchee Valley is a small part of the Osceola Plain.
The intermediate region occupies most of the middle part of the county between the lowlands and the highlands. Altitudes range from 35 to 105 feet above msl but are mostly between 50 and 85 feet above msl. A characteristic area of ridges and intervening lower areas parallel the Atlantic coast is best developed in the area between Orlando and the Econlockhatchee River. These ridges are believed to be fossil beach ridges from higher stands of the sea. The intermediate region coincides, in general, with Puri and Vernon's (1964, figure 6) Osceola Plain except for the area in the northwestern part of the county which is a part of Puri and Vernon's Central Valley.
The highlands occupy the western part of Orange County with an island outlier in Orlando and vicinity. Altitudes are generally above 105 feet but range from about 50 feet in low spots, such as the Wekiva River basin, to about 225 feet above msl near Lake Avalon on the western border of the county. The highlands contain many lakes and depressions, most of which do not have surface outlets.
The highland regions in Orange County include parts of Puri and Vernon's Orlando Ridge, Mount Dora Ridge, and Lake Wales Ridge.
The three topographic regions described above are approximately equivalent to the Pleistocene terraces postulated by MacNeil (1950) as the Pamlico terrace from about 8 feet to about 30 feet above msl, the Wicomico terrace from about 30 feet to about 100 feet above msl, and the Okefenokee terrace from about 100 to 150 feet above msl.
Cooke (1939, 1945) has called the surface defined by the 42and 70-foot shorelines the Penholoway terrace and the surface defined by the 70- and 100-foot shorelines the Wicomico terrace. The areas in Orange County that are above 150 feet probably are sandhills or altered remnants of higher terraces.
The water resources of Orange County are directly related to the topography of the area. In general, the highlands are the most effective natural ground-water recharge areas. They have few surface streams but have many lakes and depressions. The intermediate region ranges from good to very poor as a groundwater recharge area. There are many lakes in some areas and none