From an AP report at the link below:
The ever-changing thermal geology of Yellowstone National Park has created a hot spot that melted an asphalt road and closed access to popular geysers and other attractions at the height of tourist season.
The photo above shows melted asphalt on a road in Yellowstone National Park.
Park officials warned visitors not to hike into the affected area, where the danger of stepping through solid-looking soil into boiling-hot water was high.
This is not unusual as naturally changing thermal features often damage Yellowstone's roads and boardwalks.
Steaming potholes in asphalt roads and parking lots are fairly common.