Oscar Gandarilla called his son out of school Thursday in Rawlins, Wyo., and the father-son duo made the long trek south to Coors Field — all to hear snippets of a single song one last time. Yes, the 36-year-old Denver native wanted to get a final in-person glimpse of his favorite Rockies player, Charlie Blackmon, and the beard, hard-nosed approach and sweet lefty swing that’s defined the icon’s Colorado tenure. But it was more than that as Blackmon, 38, was set to retire at the end of the week.