There are a total of 3 Sand Islands in the game; two are located near the Safari and a third can be seen off the coast of the Spawn Area.
One user of this Wikia found a song in Defaultio's inventory called Bassa Islands, which has lead many of us to believe that one or all of these islands may be named Bassa Island/Archipelago. However, Defaultio has recently added the music Montauk Point to them, which may falsify this theory.
The islands are inhabited by Palm trees. The islands are made up of the "sand" material, and have a pale-yellow color. Each island connects to the Ocean floor.
There are currently only two legitimate ways to get to these islands, other than exploits or carrying an Elm tree. These methods include stacking trees on top of each other in the water to create a bridge or using a glitch that involves using a car and a chair.
One additional option to get to the Sand Islands requires another player and using a flying technique involving two logs. Both players lift the others' log up and fly to the islands over time. This option, however, may get patched in upcoming updates.
Using exploits to get to these islands can result in an instant ban. Do not attempt hacking unless you wish to risk getting banned.