NPS will use a federal channel and channels in the fed range on vhf and may also utilize local systems if a agreement is in place for dispatching and running inqueries to platrs. Some will stick to the local county or system the park is in for traffic stops and mutual aid etc and also use the vhf for localized park operations. Some will call out on both vhf and a local system for traffic stops or law related duties others stick to local systems but use NPS vhfs for basic operations. All NPS units across the US have a zone with federal vhf and a NPS LAW channel however this channel is strapped. Last bunch of new vehicles I seen had the vhf radios going to be sent to a few park regions with extra console slots for local radio equipment once they got to the destinations. The zones in the federal vhf mobiles all had the common federal zone channels.