Signage and names around this trail can be a little confusing; the trailhead sign says Ptarmigan Lake, but the trail you're actually starting on is officially known as the Ptarmigan Creek Trail. The Ptarmigan Lake trail comes later, once you've actually reached the lake — and is often so overgrown that most people skip it.
However, regardless of what the sign says, you're on the right track for the hike to Ptarmigan Lake. The campground this trail starts in also makes a fine place for an overnight stay, either before or after your hike — or some people pack a tent and camp in the primitive campsites scattered near the lake itself.