Even with about a month left in 2015, it’s already been a record-setting year for visitors to Rocky Mountain National Park. Just over 3.9 million people visited the park between January and October – topping 3.4 million in 2014. Park officials say the number could easily top 4 million if trends continue.

"When you look back at what our visitation was last November and December [2014], we had roughly 170,000 people during those last two months," said park spokeswoman Kyle Patterson. "Given that we’re already really close, we’re assuming that we will likely hit the four-million mark – if not by the end of November, then certainly by the end of December."

At this point the park is less than 60,000 visitors away from hitting that milestone.

So why is Rocky putting up such big numbers for 2015 compared to other years?

It’s likely a combination of several factors, Patterson noted, including the park’s Centennial celebration, which garnered plenty of regional and national attention. The special 100th anniversary signs have been an especially big draw. (If you haven’t gotten your selfie yet, better hurry. The signs are up until Jan. 1, 2016.) Other national parks also have seen an increase in visitors during their centennial years. In addition, low gas prices and the improving economy have prompted a rebound in travel to a number of national parks, including Rocky.

Credit NPS, Rocky Mountain National Park Facebook page / NPS, Rocky Mountain National Park Facebook page Park rangers and staff help celebrate Rocky's 100th anniversary.

There is another factor that Patterson said could be playing a role – the changing demographics of the Front Range.

"We’re seeing this increased population in Northern Colorado," Patterson said. "And we’re certainly a very handy national park for an increasing population to access."

The number of visitors to Rocky Mountain National Park has largely reflected the upward trend of the Front Range’s overall population growth in recent years. There have been some off-years – 2013, for example, where the September floods and the October government shutdown severely limited access.

More tourism to national parks is generally seen as a good thing, but at the same time, park officials are mindful of the impacts of an ever-increasing number of visitors. More resources may be needed to protect trails and habitat, but also to protect aspects of the overall experience like safety and parking.

"We hope that most of the visitors are still having a quality experience when they come to Rocky," Patterson said."That’s very important to us."