This is the wiki about the Saga of the Pliocene Exile by author Julian May starting with the book "The Many-Colored Land" and leading to books of the Galactic Milieu Series.
The Pliocene Exile and the Galactic Milieu
In the advanced technological future of the Galactic Milieu, the time-gate created a place of escape, exile, mystery, and wonder. A one-way time portal to the pre-historic Pliocene period of Earth's past between roughly 3 and 6 million years ago, it offered for some an adventure, a change, or a new life for those who didn't belong or couldn't cope with the present. Through it went the anachronists, the criminals, the misfits, and some of the most interesting figures of the Galactic Milieu. What they found there was wholly unexpected and what happened there had effects that rippled forward to the present and the future from far in the past.