Amid tree-lined paths and often startling natural beauty, much of the butte remains fenced off with rusty chainlink, visitors warded away by faded signs marked "No Trespassing" that are tacked mysteriously high in trees. And while you encounter very few hikers, you do find fast-food wrappers and spare socks, foreboding signs you're not the only one who's found their way uphill into air silent except for the soothing rush of the freeway and the occasional lone crow.