Colorado lawmakers who helped double the number of national parks in the state over the past two decades agree the state’s national parks are treasures in both economic and symbolic ways. But the conversation on public lands becomes more complex when talking about the future. The days of designating large, new national parks may be gone for an agency that struggles under budget constraints, and granting special protections for public lands is getting more contentious. As the National Park Service celebrated its centennial this week, The Denver Post interviewed four former senators from Colorado to discuss their involvement in creating national parks and their perspectives on protecting public lands.