Robert Silverberg 
Tom O’Bedlam [PDF ebook] 

A tortured man’s visions hold the key to mankind’s future in Robert Silverberg’s post-apocalyptic masterpiece   Life in the blasted wasteland of 2103 California is nasty, brutish, and short. If the savage “scratchers” don’t kill you, the poisoned environment will. But one man wanders this desolate landscape and sees beauty: glorious visions of impossible places and majestic beings not of Earth. Scorned and mocked as a madman, Tom doubts his sanity until his visions mysteriously begin to spread to others and a returning star probe offers evidence that they are real. Now, as a new religion is born, with Tom as its reluctant messiah, violent forces are unleashed—forces that have the power to transform humanity . . . or destroy it.