In his explorations, Solomons correctly determined the courses of the upper branches of the San Joaquin River. In 1892, accompanied by Joseph Nisbet LeConte and Sidney I. Peixotto, he crossed from Mount Lyell by way of Rush Creek to the base of Mount Ritter and ascended the peak. In 1895, Solomons took his most notable trip, accompanied by Ernest C. Bonner. Ascending the South Fork of the San Joaquin they came to the group of mountains now designated the Evolution Group, named by Solomons. The highest of these he called Mount Darwin (after the evolutionist Charles Darwin), and the others he named Haeckel, Wallace, Fiske, Spencer, and Huxley, after famous evolutionists of the day. Continuing their explorations, Solomons and Bonner ascended Mount Goddard, then made their way down to Simpson Meadow via North Goddard Creek, and were the first to make this section known.