OR 120 runs from a Union Pacific railroad crossing near North Columbia Boulevard to an interchange with Interstate 5 (I-5) and OR 99E.

About half of a mile (0.8 km) from where the highway begins, OR 120 crosses the Columbia Slough Bridge.

OR 120 continues to follow BNSF Railway tracks and passes through wetlands before having a T-intersection with North Marine Drive.

[1][4][5] The road continues southeast as North Marine Drive, following the Columbia River shoreline.

[7] The entire length of OR 120 is part of the National Highway System,[8] a network of roads important to the country's economy, defense, and mobility.