Any government gob you apply for is through the USA Jobs website. With the Forest Service you usually have to apply months in advance. The deadline for many seasonal positions has already passed. I am not sure about when Beura of Land Management (BLM) and Natural Resource Conservation Services Apply (NRCS) for seasonal positions, but if I were you, I would create an account on the USA Jobs website and start looking for seasonal positions now. There are all sorts of positions available in recreation, range, forestry, and biological sciences.
Be expecting to work hard. We worked 4 days a week 10 hours a day. Some mornings in June were cold, and some days in July were very hot. You just have to prepare accordingly for the whether and deal with it. You also have to become Idaho State Department of Agriculture (ISDA) certified to apply herbicides. There is a safety test that includes 50 questions, and a Agricultural Herbicide test that is 100 questions. My first month on the job, much of my time was spent studying for these tests. You can find study material on the ISDA website. Once you find out you have the job, begin studying immediately so you are ready to take the tests. The tests are more difficult than you would think. There is some math involved with conversions for calibrating spray equipment and mixing chemicals. The safety test was not as difficult as the Ag Herbicide. I had to take the Ag herbicide twice before I passed. You have to pass with at least a 75%. You will need this license to spray on your own, and also to use Restricted Use Pesticides (RUP's).