Try this day hike as an introduction to Mount St. Helens for visitors who’ve never been here, or if they haven't been in a long time.
Head left from the trailhead and stop at the interpretive signs along the way that describe the formation of the hummocks — large mounds of volcanic rock and gravel. After a shy mile keep left on the Boundary Trail to ascend to Johnston Ridge, hiking three miles to the Loowit Viewpoint and another shy mile to the Johnston Ridge Observatory.
The trail here is exposed, so bring plenty of sun protection and water. The views of the broken mountain and the bare plains surrounding it get more dramatic with every step!
Escape the heat and refill your water bottle in the Observatory, or listen to a presentation by one of the knowledgeable rangers.
On your way back, keep left at the junction with the Hummocks Trail to complete the loop along the North Fork Toutle River, and then through marshlands and young forest back to the parking lot.
Going further: As you see early in your hike, the Hummocks Trail is also the start of the Boundary Trail, stretching to the east for 57 miles to Council Lake in the heart of the South Cascades.
With some advance planning and permits in hand, experienced backpackers can include the Boundary Trail on loop trips of the Loowit Trail around Mount St. Helens itself, or the Lakes Trail through the Mount Margaret Backcountry.