The two towns are only about three and a half miles apart in Eastern Pennsylvania, separated by the Blue Mountain. Palmerton is north of Lehigh Gap, where the Lehigh River flows through the mountain, and Slatington is to the south. The two towns developed a fierce sports rivalry as sports teams (baseball, basketball, football) began to be organized in the early twentieth century.
Slatington was incorporated as a borough in 1864, but settlement of the site dates back to the mid-eighteenth century.
Palmerton was incorporated as a borough in 1912, but settlement of the area also dates back to the mid-eighteenth century.
Both towns were essentially one industry towns with Slatington centered on slate quarrying and manufacturing with many different slate companies, while Palmerton was centered on the the two plants of the New Jersey Zinc Company.
Both towns were similar in size. Using the 1930 and 1970 US census figures, Palmerton's population (Wikipedia) in 1930 was 7,678 while Slatington's (Wikipedia) was 4,134. In 1970, Palmerton was at 5,620 while Slatington was 4,687.
Both communities had sizable immigrant populations (Welsh for Slatington; Eastern Europeans for Palmerton).
When you look at the size of high school graduating classes for the two high schools over these years, you can see how close they were in size.
1934 Slatington graduating class of 106, Palmerton class of 109
1935 Slatington graduating class of 103, Palmerton class of 102
1936 Slatington graduating class of 101, Palmerton class of 100
1973 Slatington graduating class of 150, Palmerton class of 150 graduates
1974 Slatington graduating class of 125, Palmerton class of 161 graduates
1975 Slatington graduating class of 163 (170), Palmerton class of 153 graduates
Map of the Slatington/Palmerton region with a line indicating the three mile distance between the two towns.
Map of Pennsylvania with Slatington/Palmerton indicated by the small black dot above Bethlehem