After conducting thorough research, it appears that there is no boat ramp named Twin Falls Grade 3670 in Twin Falls County, Idaho. Therefore, it is impossible to discuss the characteristics of the boat ramp, such as its width, the body of water it services, and the types of watercraft permitted on the water.

It is crucial to verify the accuracy of the information before presenting it to the public, especially when it comes to geographical locations that could impact safety. It is recommended to use reliable sources, such as official government websites or local news outlets, when searching for information about a specific location.