The National Elevation Dataset (NED) contains detailed elevation data for the United States and Territories. The NED comes in three different versions.
1 and 2 Arc-Second – This version has a resolution of approximately 30 meters (60 meters for Alaska) and covers all of the United States and Territories.
1/3 Arc-Second – This version has a resolution of approximately 10 meters and covers a large portion of the Continental US only. This is more detailed than the 1 and 2 Arc-Second version.
1/9 Arc-Second – This version has a resolution of approximately 3 meters and covers only a small area of the Continental US. This is the most detailed data and is obtained from laser radar (LIDAR). This elevation data is accurate enough to make out structures and road footprints.
More information regarding the three versions can be found here.
To access the NED data, simply open the file beneath the screenshots. Then select the version you want to view. You will need to manually navigate to the area of interest or you might get a red X on the screen. Also, some of the layers will not be visible if you are not zoomed in close enough to the Earth’s surface.