For 5 miles (8.0 km) above its mouth, Solomon River flows across the coastal plain in a broad trench.
Above the coastal plain, the river occupies a comparatively broad valley and the gradient increases to at least 50 feet (15 m) to the mile.
In the floor of this valley, the river is entrenched, leaving a system of gravel terraces from 20–50 feet (6.1–15.2 m) above the water.
Gravel bars from 100–500 feet (30–152 m) wide, only partially covered at ordinary stages of the water, fill the river bed.
Jerome and Manila creeks are two short western tributaries of Solomon River within a few miles of the coast, heading within the coastal plain.