Looking at the content you have on your site (Hiking events/meetups and trail cleanups). An easy way to get links/promotion would be to give your users an easy way to promote the event they just created (give them a copy and paste embed option for their own site, and or create a wordpress plugin that allows them to have new events auto posted on their sites).
If you don't have many users do research on clubs/organizations already planning trips, but not using another tool to effectively create events and contact them to see if a plugin or embedable version would be helpful to them and if they're interested can they join the test group (this will build your user base and help you build a better experience for your users).
Another option would be to look for groups that would likely want to help out and promote your trail cleanups. Contact them and let them know about the event and make it easy for them to promote to their members if their interested. This will be great for your users because it will generate more people at their event, and it will help get the word out about your site.
Those are the ideas off the top of my head, but if you take some time and think about the opportunities are plentiful.