Julian May's four-volume Saga of the Pliocene Exile has long been one of my favorite fantasy series. It kicks off with the Many Colored Land.
May quickly introduces a future where psychic powers of various styles and strengths are common among humans and their alien friends. Humanity has developed to the point where the rest of galactic civilization is willing to take a chance and welcome us into their open and 'free' culture. Welcome to the Galactic Milieu where everyone is empowered and free to think generally what they want, so long as its within acceptable thresholds! Humans who haven't developed psychic talents yet aren't thrilled to be low beings in the evolutionary totem pole, and they seek a way out. That path turns out to be a one-way time portal into the Earth's Pliocene era.
We meet Team Green, a group of non-psychic humans looking to escape into Earth's past. They assemble the small amount of personal gear they are allowed to bring with them, each member a fanciful cosplaying survivalist, and prepare to be wholly responsible for themselves. Some are focused on building a new life and some merely see this a pleasant suicide. Once they've gathered their kit and been given some basic survival instructions, they go Back in Time!
What they find waiting for them, and what happens next, truly is a tale worth the eons (and nine novels!) through which it is told. The plots and intrigue span millions of years! The Saga of the Pliocene Exile (the Many Colored Land, the Golden Torc, the Non-Born King and the Adversary,) is followed by tales leading up to humanity's acceptance into this great interstellar psychic community, The Intervention (The Surveillance and the MetaConcert). The final three novels (Jack the Bodiless, Diamond Mask and Magnificat) comprise The Galactic Milieu trilogy, where we see humanity come to terms with its own bad self.
I'm a huge fan and think Julian May's The Many Colored Land is can't-miss fun.