The vast majority of Prospect Avenue was rechristened Hollywood Boulevard in 1910, but a modest chunk of the old Prospect still remains. One source says it was named by a former prospector (get it?) named John Bower. In 1873, Bower purchased some 160 acres in the Cahuenga Valley. He later sold 120 of those acres to four men, who in turn sold the land to Harvey H. Wilcox in 1886. Wilcox then subdivided the land as Hollywood and the rest is history. I haven’t found any other sources that support or refute this “John Bower named Prospect Avenue” claim, but I can say that Los Angeles had at least three Prospect Avenues in the late 19th century; this one was first mentioned in the press in 1887.