From the trailhead, climb switchbacks steadily through an avalanche path full of wildflowers in early summer. Soon, enter tall timer and continue climbing until you arrive at a flat section in a meadow, at a junction with the ever-popular Yellow Aster Butte trail, one and a half miles from the trailhead.
Hang a right here, and continue another half mile up to Gold Run Pass. Here, you're 1800 feet higher than the trailhead, and you can enjoy huge views from the pass. Look northeast and you can see Mount Larrabee (a reddish pyramid) and the American Border Peak. The border is also obvious, thanks to a line of logged trees on the American side. In fall, the meadows below the pass are gorgeous with vibrant gold, green and reds in the fall. Even Shuksan visible, a spectacular view on a clear day.
If Tomyhoi Lake is your destination, it's another 2 miles and 1600 feet of elevation loss to the lake, and it's worth noting that north side of Gold Run Pass is steep and exposed, and can hold snow into late summer. Bring ice axes and traction on your boots if you intend to descend to the lake. The last section of trail here can be brushy and tricky to navigate.
Gold Run Pass is a great picture spot and awesome lunch rest area; no shame if you stop here. If the steep plunge to the lake seems disheartening, about a quarter mile from the pass, there is a new trail linking to Yellow Aster Butte; a fun side trip if you have the time and energy.
To the northwest, spot Tomyhoi Peak, another 1800 feet of elevation away via a climbers path.