The US National Park Service is holding several forums around the country this month and listening to park users of all types (including mountain bikers). The meetings are designed to solicit public input into park management issues so show up and be heard! Scheduled stops in March include Alaska, Texas, Colorado, California, Florida, Ohio, Wyoming, and New Mexico. This IMBA press release has more info including dates and recommended talking points.
As you may or may not know, National Parks have only recently begun to allow off-road cycling in a select number of locations. Voicing your input can help improve the chances that your nearby park will have MTB options in the future!