This is multi-use and the only time I've blasted it was during the annual 12 Hours of Humboldt race, so it was closed to other users. Certainly it is prone to have objectionable events occur amongst the plethora of raccoon people whom intermittently step out of the ferns in their skewed ranting stewardship kind of way.
The trails are constantly expanding and it is a combo of fire trails and single track, with new single track coming into play every year. http://www.cityofarcata.org/images/stories/arcata_community_forest_trails_map_6-9-2008.pdf
The locals talk in terms of trail number..and #3 is the start climb for the race and a good point to go...500ft in .5 miles, but it will set you up for more moderate climbs and fun downhills runs. The canopy is made of ancient redwoods and a carpeting of ferns...one rider called it best ...MTBing into a huge salad bowl. The single track is nice, tight and flowing, the fire trails that connect them are in great condition with some gravel spread for erosion control. Plenty of turns that will have a reducing radius ...so if your bombing be ready to cross it up. Many of the single tracks will be at 90 degrees to the fire trail and the vegetation is so think that you'll miss them if you aren't riding with local knowledge or a race arrow.
The temp under the canopy is pretty constant and with a high level of cool humidity. Tire selection isn't so important as the trails are mostly humus.
On race day the range of tires were from Small block 8s to 2.35 Rampages.
Any water crossings are accomplished on narrow bridges.
This trail network will have me coming back to this corner of Ca fro endurance racing for years to come.
As always, show courtesy and respect to the other trail users and they'll reciprocate.