While busy with these exhibitions and scientific corps duties, during the 1860s to 1880s, he was also a much sought-after expert witness, testifying in court over the geology of mineral deposits. Among the disputes he was called into were the multiple lode theory on the Comstock, the famed Emma mine scandal in Utah, the Silver King mine and Contention mine disputes in Arizona, over tin mines in the Black Hills of South Dakota, and many others. Clark Spence recounts how his desire for the coveted U. S. Mining Commissioner appointment was lost to Rossiter Raymond because of Blake's opinions given in court against a mine owned by one of Nevada's U.S. Senators. Blake's extensive collection of diaries now at the Arizona Historical Society archives chronicle the work performed in the interest of mining corporations. One of Blake's greatest failings was the Walnut Grove disaster in Arizona. In 1886-7, Blake was hired to design a dam and water system for a hydraulic gold mining works along the Hassayampa River in central Arizona. Blake, in conflict with the promoters, quit, but the resultant shoddy work was, by some people, blamed on him, especially after the dam burst in 1890 during an Arizona freshet and several people were killed.