High level terraces representing former valley bottom deposits exist along Yukon River and several of its tributaries. The terraces contain fluvial gravel deposits wich are veneered by loess. Soil development in the gravel suggest they predate the oldest Pleistocene glaciation in central Yukon..
These high terraces are given a Neogene age (Miocene-Pliocene) based on their relative heights and the ages of bedrock that they occur on. They may be the same age as White Channel gravel in Klondike area.
Along Yukon River their elevation varies from 43 to 88 m (140 ft to 290 ft) above present river level rising to the north. Flow directions based on imbrication measurements in pits indicate flow generally followed that of the modern Yukon River. The paleo-Yukon River flowed to the nroth when these gravels were laid down.
The reason why terrace elevations rise in elevation northward, opposite to the present drainage is presumed to be from tectonic warping. The area around Dawson was uplifted more than that near the mouth of Stewart River.
Placer gold was recovered in small quantities from test pits at several sites along the Yukon River and Sixtymile River valley. The gold is typically flat, fine grained and far-traveled; suggestive of deposition in a bar environment. The number of gold particles in gravel samples (each sample 23 litre volume) ranged from 0 to 1 in Sixtymile River valley and 0 to 12 in Yukon River valley terraces. Downcutting of Yukon River and its tributaries led to placer accumulations in the modern creeks. Highly anomalous arsenic in sediment soils from Ten Mile Creek drainage with coincident anomalous gold suggest gold-arsenopyrite veins as sources for placer gold in that creek.