For almost 150 years, travelers have left messages at the “Post Office” rock formation in Ausable Chasm in the Adirondacks.

A mile-long gorge cut by the Ausable River, Ausable Chasm was a thriving industrial center during the mid-19th century. Power for iron mining and logging was aided by the rushing Rainbow Falls at the head of the gorge, and many mills and factories lined the river. Industry in the area began to wane toward the end of the century, the final nail in its coffin coming in 1890 when a large nail factory shut down. Several movies were filmed there in the early 1900s, including Perils of Pauline.

Inside are rock formations with names like the Devil’s Oven, Elephant’s Head, the Cathedral, and Column Rock. There is one particularly popular spot, where the rocks are porous and naturally divided into little cubby holes, called the Post Office. Ever since the chasm was opened to the public in 1870, visitors would climb down to tack messages into the soft rock that was formed into these little square “mail boxes,” with notes and letters going back and forth between family, friends, and hikers.

Decades of tacks took a toll on the soft rock, so to avoid further erosion a station for a logbook was built in 2004, so new visitors can still use the Post Office, but now more environmentally friendly. Human-made erosion isn’t the only way the chasm has suffered in recent history. The year 1996 saw two of the worst periods of flooding recorded in the area, with back-to-back washing out of roads and bridges and extensive damage to infrastructure. Hurricane Irene in 2011 was even worse, but the owners rebuilt, and Ausable continues to draw visitors down into the chasm to hike, go rafting, rock climb—or just leave a message.