Posey Island

Posey Island State Park is Washington's smallest marine state park, encompassing just one acre of forested land in the San Juan Islands. Located in Roche Harbor near the north end of San Juan Island, this tiny gem is accessible only by boat, typically via kayak, canoe, or small watercraft. Despite its diminutive size, Posey Island offers visitors an intimate island camping experience with stunning views of surrounding waters and neighboring islands. The park features a single primitive campsite and a minimal trail system encircling the small island. Named after early island resident William Posey, the park preserves a piece of San Juan Islands natural heritage while providing a unique destination for paddlers exploring the archipelago. The island serves as an important example of how even the smallest protected areas contribute to the conservation of the Salish Sea ecosystem.

Despite its small size, Posey Island supports diverse marine and terrestrial wildlife characteristic of the San Juan Islands. Harbor seals and river otters frequently visit the rocky shoreline, while bald eagles perch in tall conifers scanning for fish. The surrounding waters host rich marine life including kelp forests that provide habitat for numerous fish species. Seabirds such as gulls, cormorants, and pigeon guillemots nest on nearby islands and forage in adjacent waters. Black-tailed deer occasionally swim to the island from larger neighboring islands. The intertidal zone teems with purple sea stars, green sea anemones, barnacles, and various crab species. During summer months, orcas may pass through nearby waters, with both resident and transient pods utilizing the region. Songbirds including chickadees, juncos, and warblers inhabit the forest canopy. The island's position in the productive Salish Sea makes it an important part of the broader marine ecosystem.

Posey Island features typical San Juan Islands coastal forest vegetation dominated by Douglas-fir and madrone trees, with some specimens showing the gnarled, windswept forms characteristic of exposed island locations. The understory includes salal, oceanspray, and Oregon grape creating dense thickets between the trees. Sword ferns and mosses carpet the forest floor, thriving in the shade and moisture retention provided by the canopy. Coastal strawberry and various grasses occupy openings and the forest edge. The rocky shoreline supports intertidal seaweeds including rockweed and sea lettuce adapted to regular tidal inundation. Limited soil depth and exposure to salt spray influence vegetation patterns, favoring drought and salt-tolerant species. Spring brings modest wildflower displays including shooting stars and chocolate lilies in small openings. The island's vegetation reflects the rain shadow effect of the Olympic Mountains, with drier conditions than the Washington mainland coast.

Posey Island consists of glacially-sculpted bedrock overlain by thin deposits of glacial till and marine sediments. The island is composed primarily of metamorphic rocks of the Orcas Chert formation, part of the complex geological assemblage making up the San Juan Islands. These rocks formed hundreds of millions of years ago and were later uplifted, folded, and faulted by tectonic processes. The most recent Vashon glaciation scoured and shaped the island, creating its current low profile and smoothed bedrock surfaces. Glacial erratics scattered on the island were transported from distant locations by ice sheets. The shoreline features a mix of exposed bedrock, gravel beaches, and scattered boulders shaped by wave action and tidal currents. The island sits at an elevation of only 20-30 feet above sea level, making it vulnerable to wave action during storms. Ongoing erosion continues to shape the shoreline, particularly during winter storm events.

Posey Island experiences a mild maritime climate typical of the San Juan Islands, with relatively dry summers and wet, mild winters. The region lies in the rain shadow of both the Olympic and Vancouver Island mountains, resulting in annual precipitation of only 25-30 inches, significantly less than surrounding mainland areas. Summer temperatures typically range from the mid-50s to low 70s°F, while winter lows rarely drop below freezing. Fog is common during summer mornings, often clearing by midday. Winds can be significant, particularly during fall and winter storm passages, creating challenging conditions for small boat navigation. The island's exposed position makes it susceptible to wind and waves from multiple directions. Snow is rare and typically melts quickly. The moderate climate allows for year-round recreation, though summer months from June through September offer the most reliably calm conditions for paddling access.

The San Juan Islands, including the area around Posey Island, have been inhabited by Coast Salish peoples for thousands of years, with the Lummi and Samish nations having historical connections to the region. These indigenous communities utilized the islands' abundant marine resources and established seasonal camps. The island is named after William Posey, an early non-native settler who arrived in the San Juan Islands in the late 1800s. During the Euro-American settlement period, the San Juan Islands saw activities including fishing, farming, and limestone quarrying. The islands gained international attention during the Pig War boundary dispute between the United States and Great Britain in the mid-1800s, though Posey Island itself played no direct role. By the early 20th century, recognition of the islands' scenic beauty and ecological importance led to efforts to preserve key areas. The small size and limited development potential of Posey Island likely contributed to its eventual protection.

Posey Island became a Washington State Park in 1969, acquired to preserve the island's natural character and provide a unique camping destination for small boat users. The park was developed with minimal facilities consistent with its small size and boat-access-only nature. A single primitive campsite was established with a fire ring and basic amenities. The park has been managed to maintain its undeveloped character while providing safe access for kayakers and boaters. Over the decades, Posey Island has become a beloved destination for paddlers exploring the San Juan Islands, valued for its intimate scale and relative solitude. Maintenance focuses on erosion control, invasive species management, and protecting the island's natural resources from overuse. The park exemplifies Washington's commitment to preserving even very small parcels that contribute to the marine parks system. Despite its tiny size, Posey Island fills an important niche in the constellation of San Juan Islands marine state parks.

The primary attraction of Posey Island is the experience of camping on a one-acre island surrounded by the scenic beauty of the northern San Juan Islands. A short, informal trail circles the island perimeter, allowing visitors to explore the entire shoreline in just a few minutes. The rocky and gravel beaches provide opportunities for tidepooling during low tides, revealing colorful sea stars, anemones, and other marine invertebrates. Views from the island encompass Roche Harbor, nearby islands, and on clear days, the peaks of the Cascade Range and British Columbia mountains. The single campsite, located in a small clearing among the trees, offers an intimate and primitive camping experience. Kayaking and paddling in the surrounding waters provide opportunities to explore nearby coastlines and observe marine wildlife. Sunset viewing from the island's western shore is particularly spectacular. The island's small size means visitors can thoroughly explore it during a short stop or settle in for a longer stay.

Posey Island is accessible only by boat, typically kayak, canoe, or small motorized craft, with most visitors launching from Roche Harbor on San Juan Island or other nearby points. The park provides no docking facilities; visitors must beach their boats on the gravel and rock shoreline. One primitive campsite accommodates a maximum of two tents, operating on a first-come, first-served basis with no reservations. A fire ring is provided, though visitors should bring their own firewood as none is available on the island. A composting toilet serves visitor needs, but there is no drinking water—all water must be brought in by boat. The park is open year-round, though access depends entirely on weather and sea conditions. Strong currents and tidal flows around the island require paddlers to have appropriate skills and local knowledge. A Discover Pass or Cascadia Marine Trail permit is required. The nearest services and supplies are available in Roche Harbor and Friday Harbor on San Juan Island.

Management of Posey Island focuses on protecting its fragile ecosystem while providing appropriate low-impact recreation for boat-based visitors. The single campsite design prevents overuse and concentrates impact in a limited area, allowing the rest of the island to maintain its natural state. Visitors are required to follow Leave No Trace principles, packing out all trash and human waste if facilities are unavailable. Fire regulations are strictly enforced to prevent wildfire risk and protect vegetation. Invasive species monitoring targets both terrestrial plants and marine organisms that could disrupt the island's ecology. The rocky shoreline and forest vegetation are monitored for signs of erosion or degradation from foot traffic. Educational materials emphasize the importance of protecting even small islands as part of the broader Salish Sea ecosystem. Coordination with the Cascadia Marine Trail network promotes responsible paddling practices and marine conservation. Long-term stewardship aims to maintain Posey Island's character as a primitive, minimally-developed marine park for future generations.