The elevation typically ranges from 0 to 8 feet ( 2.4 m ) above sea level .
A Calusa - built shell mound on the Gulf Coast rises 20 feet ( 6.1 m ) above sea level .
The elevation typically ranges from 0 to 8 feet ( 2.4 m ) above sea level , but a Calusa - built shell mound on the Gulf Coast rises 20 feet ( 6.1 m ) above sea level .