Whether you are stationed overseas or live in the middle of nowhere, you may still be able to further your education. In addition to testing out of classes for credit and looking for online programs (such as those offered by California), you can look for education resources in the area in question.
Libraries and educational support programs on military bases can play a role, such as proctoring exams for distance learning.
Colleges nearby may have satellite campuses and other resources to help people in the area further their education.
Elsewhere, I put together a list of colleges and libraries for Coastal Washington. It's an area with a lot of farms, timberland, small towns and public parks. I imagine a lot of locals are unaware of many of the resources available locally.
If you start looking, you may be surprised what you find in your area.