FUTURE TENSE by Tyree Campbell

Lisa is the last survivor of six astronauts who were sent into space aboard the Laika to test the new faster-than-light drive and to explore other worlds. She was gone for 38 years, but time dilation makes her return 9,000 years later. The Earth is mostly a desert, and few humans have survived. She wants to find out why this happened. She is aided by Rachel, the Laika’s computer who has come to life, and by Elly, a reclusive Kentucky moonshiner who wants to learn more about her milieu.

They encounter a desolate land sparsely populated by disparate folk whose
societies are based on what little commerce exists. There are isolated groups of religious fanatics who enslave others. Finally Lisa’s search winds up at the long-abandoned site of Area 51, where she and her companions learn the truth about the fall of Earth.