The largest volcanic feature is the 1880-m-high Ruby Mountain which has been partially dissected by Pleistocene and post-Wisconsin glaciation.

A Yukon newspaper reported in 1898 that an eruption was occurring near Atlin about 80 km (50 mi) south of Gladys Lake.

Several recent studies, including a summary by Edwards et al. (2003) published by the Geological Survey of Canada, have determined that Ruby Mountain was definitely not the site of a historic eruption,[2] nor were the Cracker Creek or Volcanic Creek cones.

One possible explanation for the story is that placer miners found gold-bearing gravels beneath an ancient lava flow at the base of Ruby Mountain, and were actively tunneling under the old lava flow to mine the gravels.

As its name suggests, Ruby Mountain is ruby-colored due to the scoriaceous tephra that covers much of its summit and the summer sun shining off of the ruby-red flanks of the volcano may have started the rumour.