What is the “river” that separates Esperanza and Miguel?

The river is symbolic of the great divide between Esperanza and Miguel in terns of their social class. This divide disappears over the course of the novel.

But now that she was a young woman, she understood that Miguel was the housekeeper's son and she was the ranch owner's daughter and between them ran a deep river. Esperanza stood on one side and Miguel stood on the other and the river could never be crossed."