The Early Bronco event Son O' Beach actually takes place August 28 - 30th for 2009 and is held in the Tillamook State Forest on Friday and falls over to the Sand Lake Recreation area on Saturday.
Coos Bay is actually about 150 miles south of Sand Lake and almost 200 miles South of the Tillamook State Forest.
Here is a link to the Son O' Beach event website:
If you are vacationing to the South in Coos Bay earlier in the week before heading to Son O' Beach and are looking for a club to show you the areas...
There are the Umqua Valley Timber Cruisers in Roseburg, Oregon
Contact: Alan Paulson
And the Northwest Sand Dueces in Florence (sand dunes only club)
Contact: Lance Schiedler
Good luck, have fun and be safe!