Hi,
The should pull in the current taxonomy, but ‘trail’ is blank on that page. It doesn’t look like an archive page for a trail. Maybe a ‘county’ query would work better on that page, to show all the trails in a county:
[mashup query="county=@county&posts_per_page=-1"]
Also, you may want to confirm that the query variables do have the same name as the taxonomy (it’s possible for them to be different). You’d need to find the register_taxonomy call that was used to register them – there’s some info here:
https://codex.wordpress.org/Function_Reference/register_taxonomy