The reason we said either June or August because in Sept. of 2013 we were out west and visited Grand Canyon, Zion, Bryce, capital reef and sand dunes park in Colorado. WE had nice weather maybe one day cause it rained all the time all day. It was the same time when all the bad flooding was happening in estes park. The first time ever on any vacation we had that bad of weather. Never did get to see the bottom of grand canyon,very dissapponited. Anyway that is why we thought sept must be monsoon season but if aug is to then im not sure what the best month would be.We usually always vacation in sept cause of the crowds.Your thoughts please.