Geography of San Juan County, Washington

by | March 14, 2024

San Juan County, located in the northwest corner of Washington state, is an archipelago consisting of numerous islands, each with its own unique geography, climate, and natural features. Covering an area of approximately 621 square miles, San Juan County is known for its stunning coastal landscapes, pristine marine environments, and vibrant communities. Check climateforcities to learn more about the state of Washington.


San Juan County is composed of approximately 172 named islands, with the four largest islands being San Juan Island, Orcas Island, Lopez Island, and Shaw Island. These islands are part of the San Juan Islands archipelago, which stretches along the Salish Sea between the mainland of Washington state and Vancouver Island, British Columbia, Canada.

The geography of San Juan County is characterized by rugged coastlines, dense forests, and rolling hills, with elevations ranging from sea level to over 2,400 feet on the higher peaks. The islands are primarily composed of sandstone, shale, and granite, with rocky shores and sandy beaches lining the coastline.

The islands of San Juan County are interconnected by ferry routes, providing vital transportation links between the various communities and allowing residents and visitors to explore the archipelago. Additionally, the islands are home to several state and national parks, including San Juan Island National Historical Park, Lime Kiln Point State Park, and Moran State Park on Orcas Island, which protect and preserve the region’s natural and cultural heritage.


San Juan County experiences a maritime climate, with mild, wet winters and cool, dry summers. The climate is heavily influenced by its proximity to the Pacific Ocean and the surrounding bodies of water, which moderate temperatures and bring abundant rainfall throughout the year.

Winters in San Juan County are mild, with average temperatures ranging from the mid-30s to the low 40s Fahrenheit. Rainfall is common, particularly from November through March, with occasional snowfall occurring at higher elevations. Fog is also frequent during the winter months, especially along the coastlines and in the low-lying areas.

Summers in San Juan County are cool and dry, with average temperatures typically in the 60s and 70s Fahrenheit. The islands experience fewer rainy days during the summer months, although light showers and mist are still common. The long daylight hours of summer provide ample opportunities for outdoor activities such as hiking, kayaking, and wildlife viewing.

Spring and fall are transitional seasons in San Juan County, characterized by mild temperatures and changing weather patterns. Spring brings the blooming of wildflowers and the return of migratory birds, while fall sees the changing colors of the foliage and the harvest of crops such as apples, pears, and berries.

Rivers and Lakes

San Juan County is not known for its rivers or lakes due to its coastal and island geography. However, the islands are surrounded by the waters of the Salish Sea, which provide important habitat for marine life and support a variety of recreational activities such as boating, fishing, and whale watching.

Several bays, harbors, and inlets dot the coastline of San Juan County, including Friday Harbor on San Juan Island, Eastsound on Orcas Island, and Lopez Village on Lopez Island. These sheltered waters provide safe anchorage for boats and yachts and serve as popular destinations for sailing, kayaking, and paddleboarding.


The vegetation of San Juan County is diverse and includes coniferous forests, deciduous woodlands, and coastal habitats.

Coniferous forests dominate much of the islands’ landscapes, consisting of species such as Douglas fir, western red cedar, and Pacific madrone. These forests provide habitat for a variety of wildlife species, including deer, eagles, and otters, and contribute to the region’s scenic beauty and recreational opportunities.

Deciduous woodlands are also common in San Juan County, particularly in the lower elevations and along the shorelines. Species such as maple, alder, and cottonwood are common in these woodlands, providing habitat for songbirds, squirrels, and other small mammals.

Coastal habitats such as salt marshes, tidal flats, and rocky shores are important ecosystems in San Juan County, supporting a variety of marine life and bird species. These habitats provide feeding and breeding grounds for fish, shellfish, and shorebirds and play a crucial role in the region’s ecological health and biodiversity.

Human Impact

Human activity has had a significant impact on the geography of San Juan County, particularly in terms of tourism, development, and conservation.

Tourism is a major economic driver in San Juan County, with visitors drawn to the region’s natural beauty, outdoor recreational opportunities, and cultural attractions. The islands are home to several charming towns and villages, including Friday Harbor, Eastsound, and Lopez Village, which offer a variety of shops, restaurants, and accommodations for visitors.

Development pressure has increased in recent years, particularly on the more populated islands such as San Juan and Orcas. Residential and commercial developments, including vacation homes, resorts, and marinas, have altered the landscape and raised concerns about habitat loss, water pollution, and shoreline erosion.

Conservation efforts have been implemented to protect and preserve the natural beauty and ecological integrity of San Juan County. Organizations such as the San Juan Preservation Trust and the Washington Department of Fish and Wildlife work to acquire and manage conservation easements, nature reserves, and wildlife refuges for public enjoyment and environmental stewardship. Efforts are also underway to address threats such as habitat fragmentation, invasive species, and climate change, which pose challenges to the long-term health and sustainability of the region’s ecosystems.


In conclusion, San Juan County, Washington, offers a diverse array of geographical features, including islands, coastlines, and forests. The county’s maritime climate, with its mild winters and cool summers, influences life in the region and shapes activities such as tourism, recreation, and conservation. While human activity has altered the landscape, efforts to conserve and protect the county’s natural resources ensure that its geography remains a defining feature of the region for generations to come.