Denver author Chris Duerksen on Tuesday told attendees of the fifth Big Sky or Big Sprawl Conference that western Montana is looking a lot like Colorado did 25 years ago -- which in turn looks like California in the 1930s.

"It's spooky to see the growth patterns," he said. Duerksen is widely seen as one of the country's foremost authorities on growth planning.

His comments came on the heels of a presentation by Montana Smart Growth Coalition Director Tim Davis, who used a growth model developed by the Sonoran Institute to show where residential growth may expand in the next two decades in the state's fastest-growing counties.

If current regulations and growth trends hold true, residential development will continue to spread outward from urban centers like Helena, Bozeman, Kalispell and Billings -- filling mountain valleys with increasing amounts of new homes, Davis said.

Davis and Duerksen were joined by several moderators at the conference, which about 100 people -- city and county planners, elected officials, ranchers, residents and others -- attended, to answer a question Davis posed in his opening remarks: "How are we growing (and) how do we guide the growth in a way that protects what we all love about Montana?"

"We need to find a way to come together and move forward, rather than fight about the future," he added.

The conference at Carroll College covered joint city-county planning, conservation, water resources, economics, affordable housing and ways to protect urban areas in wildfire country.

Davis said inefficient development is encouraged in three ways in Montana -- the state's one-acre minimum lot size for septic systems, a water-right exemption for residential wells drawing 35 gallons per minute or less, and the lack of access management along state highway corridors.

The state's septic and well regulations encourage development to spread away from urban areas -- increasing the amount of land used for residential purposes, endangering groundwater quality and creating problems for water-rights holders, he said.

Davis said development should instead be encouraged to take place closer to cities like Helena. He showed two artist's renderings of rural subdivisions, one depicting a neighborhood of homes each on several acres of land, and another showing the same amount of homes clustered close together, with a large amount of open space nearby.

Regulations now encourage the former, but not the latter, Davis said. The state's allowance of septic systems and wells on small lots make it easy for developers to subdivide tracts into lots that spread out across the landscape.

Lewis and Clark County Senior Planner Frank Rives said the one-acre minimum lot size has long driven the density of subdivisions in Montana. The county has regulations for clustered subdivisions on the books, he said, but developers often don't go that route.

Duerksen's keynote speech highlighted the history and future of zoning regulations across the country.

"If something doesn't change dramatically with development codes, they're going to be irrelevant," he said.

He said communities are pioneering new regulations that address public health, energy, climate changes and food security.

Codes that promote the use of solar or wind energy in residential neighborhoods, rather than make those alternatives more difficult for homeowners to implement, should become the norm, Duerksen said, along with regulations offering incentives for green roofs and pedestrian-friendly development.

"It's not going to solve the global warming problem, but it's got something to contribute," he said.

Larry Kline can be reached at 447-4075 or larry.kline@helenair.com.