I live near Green Lake in Seattle and in my experience on nice days Green Lake is so crowded that people are certainly not 6ft apart consistently.
I also do a lot of hiking and on nice days the popular (and most accessible) trails are utterly packed with people. There would be no way you would be able to consistently stay 6ft apart.
Green Lake would be less crowded if those near living there could go to other parks that normally are far less crowded than Green Lake. However those other parks had their parking lots closed by the city, which means locals near you have no choice but to crowd into the running trails around Green Lake.
On the trails - I think we could easily force them to operate at half density by closing half the lot at popular trailheads. People would spread out to other locations as a result.
Even so, you don’t have to be 6 feet apart all the time. The WHO’s guidance is only 3 feet, for one. But you also get a benefit from just MOSTLY reducing contact, and even on crowded trails people aren’t on top of each other except at the destination. With mask requirements the risk is likely low.
I also do a lot of hiking and on nice days the popular (and most accessible) trails are utterly packed with people. There would be no way you would be able to consistently stay 6ft apart.