Susan is lying in bed, "looking through her journal, rewriting incidents and observations into coherent paragraphs" (5.5.1).
Apparently, Thomas and Augusta have just arrived in Mexico for a visit. Why didn't anyone tell us? The only problem is that a bunch of other people have arrived, too, like Clarence King and Bessie, which means that Susan and Oliver don't have anywherenear enough room.
Suddenly, Susan's eyes open. Wait, what? Oh, okay, we understand it now—that was a dream.
Oliver has just arrived. Susan tells him about her dream, but she can tell that something is wrong.
Turns out, the mine is no good, after all. Or, it might be good, but it'll be way too expensive for Oliver to recommend that someone invest money into it.
This causes Susan to utter an unthinkably dirty cussword: "damn" (5.5.19). That's practically the F-word for a classy Quaker like our gal Susan.
So, where else can Oliver and Susan go? Leadville is no good. Staying in Mexico is out of the question. To put it simply, they're stuck between a rock and a hard place.