Yes, the Riggs are related to Parley P. Pratt.
Through my Mom Cleo Judd's side of the family, Parley is my great-great-great-great grandfather. Some years ago I joined the Jared Pratt Family Association. Jared is the father of Parley and Orson.
I hadn't been too involved until a couple of years ago when I discovered that a prominent businessman here in Utah, Robert Grow, whom I know fairly well from my business and political associations, was the new President of the Association. I immediately contacted him and told him we were related. We now refer to other as "Cuz." I don't see him that often because he is also a prominent Democrat and has been often mentioned as someone who might run for political office in Utah.
I got an e-mail from Matt Grow, new Historian of the Association and an assistant professor of history at the University of Southern Indiana. He announced that on July 2, BYU will host a conference on Parley and Orson Pratt. Along with Professor Terryl Givens of the University of Richmond, he has been directing a seminar on the thought of the Pratt brothers. He and Terryl are currently writing a biography of Parley. They also have eight graduate students from around the nation and the world who will be presenting their research on the life and thought of the Pratts at this conference.
I can't wait, as this should be a great opportunity to delve more deeply into our Pratt ancestors.