“Muslim terror cell opened fire on campers and hikers...” is a big stretch...less sensational story here: http://losangeles.cbslocal.com/2016/03/29/17-men-reportedly-heard-chanting-firing-off-shots-in-apple-valley-detained-released/
and
http://www.freerepublic.com/focus/f-news/3415250/posts
More write-ups:
http://www.vvng.com/update-subjects-in-deep-creek-incident-detained-and-released/
http://www.vvng.com/report-of-15-men-with-guns-detained-at-deep-creek/
And the least sensational write-up (might not have been ME men at all...regular dudes with bandanas out target shooting with legal firearms): http://www.pe.com/articles/area-798307-deputies-responded.html
Even looking at that report is does all sound very strange, at best, and if you lived in that area I can see why you would call the police.