Access to controlled venues like city/state/U.S. parks can be problematic but appear to be opened for the most part (August 2020) as the U.S. struggles it way through the COVAD pandemic.
Hiking is a wonderful activity during these sequestered, social distancing, face mask wearing times. Like running and walking, hiking is available to anyone with some obvious behavioral actions. I tie a bandana around my neck, adjusted for face mask duty when passing anyone within 6 ft. One can a wear a mask continually but it may not be necessary except at parking lots, trail heads or people passing on trails. And, clearly, wearing a mask all the time is an impediment to oxygen intake.
A common protocol is to lower the mask for most of the time. When sighting a hiker/runner/biker within 50 yards, pull the mask up. The other person usually will reciprocate. Those failing to have a mask either will be suitably embarrassed, or wonder why you are being so cautious.
Wearing a mask outdoors may have another interpretation. Even though the odds probably suggest it would not be necessary, an abundance of caution sets a good example.