The Siltcoos River is a stream only 3 miles (4.8 km) long that begins at Siltcoos Lake and meanders generally west to the Pacific Ocean, about 8 miles (13 km) south of Florence and 13 miles (21 km) north of Reedsport, Oregon. The Siltcoos River is a canoe trail that passes through the Siuslaw National Forest and the Oregon Dunes National Recreation Area.

The Oregon Dunes are over 100,000 years old and stretch along 40 miles (65 km) of the central Oregon coastline. Studies have determined that the youngest dunes are closest to the ocean and began forming about 7,000 years ago. The primary source of sand forming the Oregon Dunes are sediments transported from the mountains primarily by the Umpqua and Siuslaw Rivers and deposited along the coast. Alongshore currents then transport the sand in suspension and along the ocean floor parallel to the coast. Waves and tides tend to move sand towards (or away from) shore. When waves deposit sand on the beach, the prevailing winds blow the sand up the beach face.

Dune formation is mainly dependent on the wind. In the summer the wind generally blows from the north and northwest averaging 12-16 mph (19-26 kph). Mountain barriers along the coast deflect the wind currents that form the dunes into many different shapes. In the winter the average wind speeds are generally much slower (except during episodic storms) and the direction is from the south and southwest. These winds move large amounts of sand, causing the dunes to be reshaped. Read more here and here. Explore more of the Siltcoos River here: