Although you were in a federal park when caught, the case will probably be referred to a local prosecutor's office for filing rather than the US Attorneys Office due to the relatively small quantity of drugs and what sounds like a pretty unsophisticated operation. If you have the funds, you may want to consider hiring a private attorney to start trying to figure out where charges will be referred and see if anything can be done to either prevent the filing of charges or minimize the seriousness of the charges. At the very least, no more speaking with the police or park rangers. Generally speaking, the only thing you will do by speaking to them is dig yourself in deeper.
You need a criminal defense attorney licensed and experienced in the federal courts.
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.
As we have seen in other Federal land cases, the charges may be dropped down to a local misdemeanor under state law through the ACA.
USAM 9-20.100; USAM 9-20.115
“Prosecutions instituted under this statute are not to enforce the laws of the state, but to enforce Federal law, the details of which, instead of being recited, are adopted by reference. In addition to minor violations, the statute has been invoked to cover a number of serious criminal offenses defined by state law such as burglary and embezzlement. However, the Assimilative Crimes Act cannot be used to override other Federal policies as expressed by acts of Congress or by valid administrative orders.”
So, the lesson we all learn here is if there is no lesser Federal charge available, ask the AUSA to apply the ACA using a lesser State charge if on Federal lands.
You should find an attorney who has experience defending drug cases in both state and federal court. If the other two people charged were charged in state court, it is likely you will also be charged in state court unless your possession in this instance is part of a larger drug distribution ring.
I am not your attorney and cannot give you legal advice.