We were wanting to know about how far these sights are from downtown Las-Vegas.
And also, what means of travel is most used.
Hoover Dam is about 50 miles from Downtown Vegas. Grand Canyon (South Rim) is roughly 300 miles and takes 5-6 hours to reach. The West Rim is much closer but not as dramatic.
You can only easily travel by road between the two cities. Tour buses going to both sites are common in Las Vegas, but mostly just rent cars and drive it.