Little Sucia and Sucia islands belong to an archipelago of ten islands in the San Juan Islands, including Ewing, Justice, Herndon and the Cluster Islands, plus several smaller unnamed islets, about 20 miles (32.2 km) west of Bellingham and 3.5 miles (5.6 km) north of Eastsound, Washington. Sucia Island, the largest of the group, was charted in 1791 by the Spanish naval officer Francisco de Eliza, who labeled it “Isla Sucia,” Spanish for “dirty” or, in nautical usage, “foul,” a reference to the reefs and hidden rocks that made navigation hazardous. The islands’ distinctive horseshoe shape comes from two folded sedimentary rock units, the Cretaceous-age Nanaimo Group and the younger Eocene Chuckanut Formation, bent into a syncline and juxtaposed along the Fox Cove Fault. During the last ice age a lobe of the Cordilleran ice sheet, more than half a mile thick in places, buried the region before retreating north through the San Juan Islands by about 13,000 years ago, scouring the channels between the islands and scattering the glacial erratics still found on Sucia’s beaches.

The isolated coves and bays of Sucia Island once served as seal-hunting grounds for the Lummi and other Coast Salish peoples. In the 19th century those same coves sheltered smugglers who slipped Chinese laborers into the country in defiance of federal exclusion laws, along with smuggled wool and opium. During Prohibition, in the 1920s and early 1930s, rum-runners used the islands to evade customs agents along the Canadian border, and more recently smugglers have used them for drug trafficking. Washington State Parks acquired part of Sucia Island in 1952; developers eyed the rest for vacation lots until 1960, when the Puget Sound Interclub Association, a recreational boating club now known as the Recreational Boaters Association of Washington, bought and donated the remaining land to the state, completing the marine park. Sucia Island Marine State Park covers 814 acres (329 ha) with 77,700 feet (24 km) of shoreline; it offers camping and vessel moorage across several bays but no other services, and fossil collecting is prohibited.

Fossil Bay, on Sucia Island’s southern shore, takes its name from the abundant marine-invertebrate fossils, ammonites, clams and snails, embedded in its exposed sandstone and siltstone. In April 2012 two Burke Museum research associates searching the bay for ammonites spotted a fragment of exposed bone; a follow-up excavation the next month recovered a partial left femur, 16.7 inches (42.4 cm) long and 8.7 inches (22.1 cm) wide, whose hollow marrow cavity and hip-socket placement identified it as a theropod’s. Christian Sidor and Brandon Peecook, describing the find in PLOS ONE in 2015, estimated the complete bone at more than 3 feet (1 m) long, slightly smaller than a Tyrannosaurus rex femur, and found it closely resembled Daspletosaurus torosus, though it was not that species; the discovery made Washington the 37th state with a confirmed dinosaur find. Read more here and here. Explore more of Little Sucia Island and San Juan Islands here: