Complex sentence: There, he finds a group of Samantha clones, all no older than the day the real Samantha originally disappeared in the early 1970's, working on the alien colonists' and Syndicate's joint project of spreading the Black Oil.
Split into simpler sentences: There, he finds a group of Samantha clones, all no older than the day the real Samantha originally disappeared in the early 1970's. The clones had been working on the alien colonists' and Syndicate's joint project of spreading the Black Oil.