I believe that's been established in many studies in the past but it's due to the younger cougars being forced into more populated areas by mature cougars. It happens when cougar numbers increase and more people move into rural areas.
Cougar numbers are increasing according to WA DFW in latest numbers I found (August, 1999).
Cougars, also known as mountain lions or pumas, are native to Washington state. About 2,500 live in this state, double the populations of the early 1980s, and their numbers are growing.
Last year I was ghostwriting a weekly column for an Oklahoma newspaper, and one of the columns was about the OK legislature giving approval for the WL agency there to establish a cougar hunting season.
The agency feels enough of these cougars are moving back into the state to prepare for management seasons.
Cougars are increasing in number, and their ranges are moving across state lines.