The field of membership includes all employees and volunteers of the US Department of the Interior which includes the National Park Service and several other bureaus. There are several other select employer groups. See site for details. Note, anyone can volunteer in National Parks around the country. Although this can't be done in time for this promo, it might be useful for future promos.
Branches are located in Washington DC and in Reston, Virginia. Membership can be done by mail and accounts can be opened online. Also, they participate in the National CO-OP Network. So branch visits may never be necessary.
The credit union is NCUA insured. It has $83 million in assets and 9,881 members.
Thanks to the reader who mentioned this credit union in the finding deals post.