The best trailhead for the hike is the Highline Trailhead located along State Highway 150 33.2 miles east and north of Kamas, or you could drive south from Evanston. You could also start at Mirror Lake, but you must pay to park there, and there isn't as much room to park.
This is the easiest route to the summit of Spread Eagle Peak.
From the trailhead at 10,347 feet, follow the Highline Trail 0.8 miles to the junction with the Mirror Lake Trail. The trail continues south and east and drops to 9900 feet. Scudder Lake is passed after 2.2 miles (from the trailhead). After another 0.8 miles, pass a junction with the Wilder Lake Trail. Stay left on the Highline Trail. After another 1.3 miles, turn right at the junction where the Naturalist Basin Trail branches off the Highline Trail. Follow the Naturalist Basin Trail through the beautiful basin and after another mile, hang a right at the next junction. Follow the trail another mile to Jordan Lake. From Jordan Lake, follow the switchbacking trail up to Shaler Lake.
Either Jordan or Shaler Lake makes a good basecamp. Jordan Lake is much more heavily used, but Shaler Lake is more exposed to the elements as it is right at timberline (10,920).
Shaler Lake is 7.0 miles from the trailhead and there is no trail beyond Shaler Lake. From the lake, head northwest to the base of the col to the southwest of Spread Eagle. Once at the base of the col, scramble up to it. This is the steepest and most difficult part of the route. Once at the col, scramble up the ridge to the northeast and to the summit of Spread Eagle.
The views are incredible. Dozens of peaks and lakes are visible, and there are no signs of civilization.
Hayden from the summit of Spread Eagle
A good pair of boots is needed.