NewhalemTrailsMap – is an overview map of the hiking trails around Newhalem [race site]
NorthCascadesHighwayLoop – is an overview map of showing Seattle [bottom left] relative to Newhalem and the Cascade Mountains.
HERE is an extensive list of hiking trails of various lengths in the Newhalem area available in North Cascades National Park.
There are two excellent hiking guides that cover the North Cascades, both the national park and national forest. The first is Hiking the North Cascades by Erik Molvar. The second is Day Hiking North Cascades by Craig Romano [available only in Kindle edition].
If you have free days while in the Seattle area before heading north for the race, Peter Stekel has written Best Hikes Near Seattle. There are 42 trails to choose from, all within 60 minutes or 60 miles of downtown Seattle. The book is available HERE. A Kindle version is HERE. Note: this book does not cover hiking in the Newhalem area but does include information about the natural history of Western Washington and the Cascade Mountains.