ILWACO — In this era when satellites peer down into every backyard, it’s strange to call any part of America “terra incognita.” But this old Latin term used by mapmakers — literally “unknown land” — fits the Sand Islands lying just offshore Ilwaco and Chinook in Baker Bay.

Once some of the most valuable real estate in the nation due to a prime location in the path of returning salmon, at low tide the main Sand Island is separated by about 600 feet from the southern end of the Long Beach Peninsula near “A” Jetty and U.S. Coast Station Cape Disappointment. The roughly 800-acre island is more than two miles from the nearest northwestern tip of the Oregon mainland.

East Sand Island, at 62 acres, begins about a mile west of Chinook. It is often in the news because of thousands of birds that nest there, annually gobbling millions of small salmon migrating toward the ocean. It’s intensively monitored and uninvited human guests are unwelcome.

Predatory birds don’t care so much for the bigger Sand Island, despite its beautiful 10,000-foot white sand beach that faces southwest toward the mouth of the Columbia. It is almost entirely unvisited, except for rare surfers determined to experiment with riding ship wakes or storm-generated swells. A few Ilwaco and Chinook boaters occasionally hop off to beach comb. But on maybe 300 days out of 365, a visitor will enjoy this Robinson Crusoe setting in solitary splendor.

Now lightly overseen by the U.S. Army Corps of Engineers, in the 19th and early-20th centuries it was a dramatically different scene. Hundreds of men and scores of horses pulled enormous salmon-packed seine nets to shore. Considered nearly unique to the island, horse seining once attracted international acclaim and generated hundreds of thousands of dollars a year for fishermen and packing firms.

All this money elicited a legal “battle royal” between Washington state and Oregon, with the U.S. Supreme Court siding with Oregon in 1908. Interest in the island quickly faded following decimation of the salmon runs by dams. The states formally ended their border squabble by signing an interstate compact in the 1950s.

With a mature forest, brush-covered sand dunes and dense stands of bright yellow gorse, Sand Island is a mysterious and neglected sanctuary, hiding in plain sight.

Starting with this photo feature and continuing with follow-up news coverage, we’ll be exploring the island, its wildlife and rich history.

Read more on chinookobserver.com.