Not to be discouraging, but I have observed that it can be very difficult to get hired by the US National Park Service, especially if you are interested in working in a particular park or area. One of our rangers told me she applied for about 100 jobs before she was finally hired. And expertise in a particular subject doesn't seem to have much bearing on whether or not someone is hired. You pretty much have to be willing to go anywhere and do anything to build up points and seniority. In the case of interperative rangers, the NPS seems to think that anybody can be plugged in to any park and trained in a few weeks. The ranger mentioned above said that the idea was to avoid it being an "old boy" system where people are just hiring their friends, but it seems that the actual result is that it can be very difficult to hire the best person for the job, especially if another applicant is a veteran or has some other preferential factor.

So--perserverance furthers!