Hello Jamin-
Here is a longer answer to your question "What is the angle of declination on Hood".
Magnetic Declination is the angle, east or west, to correct a magnetic compass bearing to match a printed map such as the standard USGS Quad map (for Mt Hood). Quads are printed with True (or geographic) lines.
If you are not using a map to obtain you bearings, but just taking visual bearings on a clear day with your compass from say, Illumination Rock to the parking lot at the Timberline Lodge, you do not need to correct for magnetic declination. You can use the magnetic bearing to return down the hill.
You must adjust your compass for magnetic declination if your are taking the bearing angle of a line say from Illumination Rock to the center of the Lodge parking lot from the quad map.
Each degree of error will be about 94 feet in a mile. Ten degrees off will be 940 feet. Seventeen degrees off will be 1, 598 feet off from the True Bearing in one mile!
Your GPS is set by default to magnetic bearings. If you are using your (default) GPS to give you a compass bearing angle from Illumination Rock to your GPS Waypoint (set at your rig in the middle of the Lodge parking lot) you must not use the True bearing on your compass. Use the Magnetic Bearing.
To change your GPS to True, go to set-up, north reference and select True. Note the declination that is reported on your GPS when it is set to Magnetic North. You will find it to be 17 degrees as noted by pindude.
The recommended way to handle Magnetic Declination is 1. set your GPS to True North and 2. set your compass to True North and 3. use the USGS Quad Map for your climb.
To set your compass to True North to match your map and GPS, use the brass micrometer screw on the correct kind of compass.
Purchase a $30 Suunto M3D base plate compass, a $100 Garmin eTrex GPS and a $6 GPS.
The total cost to these three functional tools is about $136. You will need to learn how to use them together from reading Freedom of the Hills or taking a Mazama, the Mountaineers or similar class.
Google the three words map compass GPS and click on the second listed six page PDF Handout to learn more about backcountry navigation on the web.
Have I made any errors? Never trust one person in your group with sole responsibility for backcountry navigation!
--trad_guy