Eccles was one of the first British mountaineers to make ascents of the higher peaks of the Rockies. On 7 August 1878, in a party of eight including surveyor Ferdinand Vandeveer Hayden, topographer A. D. Wilson and Eccles's favourite guide, Michel Payot, Eccles made the second ascent of Fremont Peak (once mistakenly considered the highest peak in the Rockies); he also climbed Wind River Peak in the Wind River Range while accompanying the Hayden Survey, together with A. D. Wilson and Payot. Eccles offers the following description of Wilson: