The Rockies’ sky-high expectations for the 2018 season rest, in large part, on their young starting rotation. All-star third baseman Nolan Arenado is excited about the rotation’s potential, but he’s setting a high bar for Jon Gray, German Marquez, Tyler Anderson, Jeff Hoffman and Antonio Senzatela. “I think they are going to be great and I think they are already pretty darn good,” Arenado said Saturday as the Rockies winter caravan concluded with a stop at Coors Field. “But I hope they understand that there is no time to rest. It’s time to get better and better.