The Lanphere Dunes lie between the Pacific Ocean and the Mad River Slough, which flows through the Arcata Bottoms at the head of Humboldt Bay, about 59 miles (95 km) south of Crescent City and 8 miles (13 km) north of Eureka, California. The area was long occupied by the Wiyot people before European settlement. The Arcata Bottoms is a low-lying area adjacent to Arcata Bay in Humboldt County, historically used for agriculture and wetlands. It lies near the city of Arcata, which was first settled as the village of Union in 1850. In the 1930s William and Hortense Lanphere made their home there and spent the next 40 years keeping the dunes largely pristine.

Coastal dunes form where sediments deposited along the shore are driven inland by onshore winds forming linear mounds of well sorted fine to medium sand accumulations. The Lanphere Dunes are built from sediments derived from the Mad River watershed of 318,080 acres (128,722 ha) and carried to the sea and eventually deposited to form part of a larger Humboldt Bay dune system that extends some 34 miles (55 km) along the northern California coast. There are various types of vegetation that grow on the dune surface and stabilize it. The dunes complex includes beach, foredune, herbaceous and woody swales, coniferous and riparian forest, freshwater swamp, freshwater marsh, brackish marsh, salt marsh, and intertidal mudflats.

In 1975 the Lanpheres joined faculty from Humboldt State University, who used the site for botany classes, in pushing for its permanent protection; the following year Hortense donated much of the land to The Nature Conservancy, which added adjoining parcels before transferring the property to the US Fish and Wildlife Service in 1997. The dunes are now part of the Humboldt Bay National Wildlife Refuge, where management focuses on eradicating invasive plants and restoring natural dune and estuarine processes. In January 2021 the Lanphere and neighboring Ma-le’l Dunes were jointly designated a National Natural Landmark. Read more here and here. Explore more of Lanphere Dunes and Arcata Bottoms here: