Rating Newest Oldest. Best Answer: Well for Vegas and the Grand Canyon sept/oct would be ideal. Not too hot. The summer months are the worst for Vegas and Grand Canyon because it gets HOT! LA would be nice in sept/oct, perfect beach weather as well.Source(s): Lived in AZ, visited Vegas 3 times, visited Cali numerous times.ating Newest Oldest. Best Answer: Well for Vegas and the Grand Canyon sept/oct would be ideal. Not too hot. The summer months are the worst for Vegas and Grand Canyon because it gets HOT! LA would be nice in sept/oct, perfect beach weather as well.