An extract on #druff
Elevation in the county ranges from mean sea level to its highest natural point of 110 feet (34 m) near the intersection of SR 580 and Countryside Blvd. in Clearwater. Due to its small size and high population, by the early 21st century Pinellas County has been mostly built out, with very little developable land left available. The county has maintained a fairly large system of parks and preserves that provide residents and visitors retreat from the city and a glimpse of the peninsula's original state.
Geologically, Pinellas is underlain by a series of limestone formations, the Hawthorne limestone and the Tampa limestone. The limestone is porous and stores a large quantity of water. The Hawthorne formation forms a prominent ridge down the spine of the county, from east of Dunedin, south to the Walsingham area and east towards St. Petersburg.
The 35 miles of beaches and dunes which make up the county's 11 barrier islands provide habitat for coastal species, serve as critical storm protection for the inland communities, and form the basis of the area's thriving tourism industry. The islands are dynamic, with wave action building some islands further up, eroding others, and forming entirely new islands over time. Though hurricanes are infrequent on this part of Florida's coast, they have had a major impact on the islands, with the Hurricane of 1848 forming John's Pass between Madeira Beach and Treasure Island, a hurricane in 1921 creating Hurricane Pass and cleaving Hog Island into Honeymoon and Caladesi Islands, and 1985's Hurricane Elena sealing Dunedin Pass to join Caladesi with Clearwater Beach.
Between the barrier islands and the peninsula are several bodies of water, through which traverses a section of the Gulf Intracoastal Waterway. From north to south they are: St. Joseph Sound between the islands and Dunedin, Clearwater Harbor between Clearwater and Clearwater Beach, and Boca Ciega Bay in the southern third of the county. Connecting Clearwater Harbor to Boca Ciega Bay is a thin, approximately 3.5-mile (5.6 km) stretch of water known as The Narrows, which runs next to the town of Indian Shores.
Extending from northeastern Boca Ciega Bay, Long Bayou separates Seminole from St. Petersburg near Bay Pines. Long Bayou once extended significantly farther up the peninsula until the northern portion was sealed off to create Lake Seminole. Extending further still from Long Bayou, the Cross Bayou Canal traverses the peninsula, crossing Pinellas Park in a northeasterly direction before emptying into Tampa Bay on the northwest side of St. Petersburg-Clearwater International Airport.