Receding Colorado floodwaters are revealing a new landscape of toppled homes, buckled highways and twisted debris -- as well as new health dangers -- while rescuers continue to hunt for hundreds of stranded citizens.  The floods have left six dead, plus two women missing and presumed dead.  As of early Wednesday morning, state officials estimated to the Denver Post that at least 600 people remained stranded in isolated areas of the state.  Health officials are warning residents who are picking through rubble to stay out of floodwaters, citing fears of contamination.  "Many contaminants, such as raw sewage, as well as potential releases of chemicals from homes, businesses and industry, may be contained in the floodwaters," Mark Salley, a spokesman for the Colorado Department of Public Health and Environment, told the Colorado Springs Gazette.  The Colorado Oil and Gas Association has shut down nearly 1,900 oil and gas wells in flooded areas as a precaution, and crews are inspecting operations to check for any leaks, the Denver Post reports.  "We have seen photos of oil slicks on top of the floodwaters and we are continuing to monitor all of the flooding and cleanup efforts," Gary Wockner, Colorado program director for the environmental group Clean Water Action, told Accuweather.  Increased amounts of standing water from the flooding is also raising concerns about the growth of mosquitoes and the risk of the West Nile virus, officials from Weld County say.  The rebuilding effort will cost hundreds of millions of dollars and is expected to take months, if not years.  County officials have started their own damage tallies: 654 miles of roads in Weld County bordering Wyoming, 150 miles of roads in the Boulder County roads foothills, along with hundreds of bridges, culverts and canals.  Northern Colorado's broad agricultural expanses are also especially affected, with more than 400 lane-miles of state highway and more than 30 bridges destroyed or impassable.  Colorado Department of Transportation's Chief Engineer Tim Harris told the Denver Post that assessment crews tried to scope out damage on some roads on Sunday but were “chased out by rain and rising water.”  More than 600,000 residents in Boulder and Larimer counties may have to wait throughout 2014 for roads to be permanently repaired, according to transportation department spokeswoman Mindy Crane.  State officials have put initial estimates at more than 19,000 homes damaged or destroyed throughout the flooded areas.  For the first time since the flooding began last week, the rain did not fall on Tuesday. The break in the weather allowed emergency crews to carry on attempting rescues of stranded residents, and anyone else who was willing to go along.  But at least 100 people in the town of Pinewood Springs were standing their ground, saying that they will rely on gas-powered generators in a bid to protect their homes from vandals, the Denver Post reports.  A man who would only identify himself as Gary told the newspaper that people staying in the town to keep watch made it easier for him to decide to leave.  "Everybody hated to leave their homes," he said. "But you start thinking about it, and you realize you can't stick around there."  Steve Novakovich, a 75-year-old Alaskan bush pilot, says he left Pinewood Springs after hosting a cookout for firefighters and rescue workers with a $700 shipment of salmon and halibut that arrived at his home before the floods hit.  In other communities, rescue crews showed residents pictures of flood-damaged roads in an attempt to get them to leave.  "Larimer County doesn't own any helicopters and won't be able to do any food and water drops," Larimer County Sheriff spokesman Nick Christensen told the Denver Post. "If they don't take this opportunity now, they may be there for a very long time."  Federal and state emergency officials, taking advantage of sunny skies on Tuesday, said more than 3,000 people so far have been evacuated by air and ground, but calls for those emergency rescues have decreased.  "They've kind of transitioned from that initial response to going into more of a grid search," Colorado National Guard Lt. Skye Robinson told the Associated Press.  In one of those searches Tuesday, Sgt. 1st Class Keith Bart and Staff Sgt. Jose Pantoja leaned out the window of a Blackhawk helicopter, giving the thumbs-up sign to people on the ground while flying outside of hard-hit Jamestown.  Most waved back and continued shoveling debris. But then Bart spotted two women waving red scarves, and the helicopter descended.  Pantoja attached his harness to the helicopter's winch and was lowered to the ground. He clipped the women in, and they laughed as they were hoisted into the Blackhawk.  After dropping off the women at the Boulder airport, the Blackhawk was back in the air less than a minute later to resume the search.  One of the missing is Gerald Boland, a retired math teacher and basketball coach who lives in the damaged town of Lyons. Boland's neighbors, all of whom defied a mandatory evacuation order, said Boland took his wife to safety Thursday then tried to return home.  Two search teams went looking for him Monday.  "He was very sensible. I find it amazing that he would do something that would put himself in harm's way," said neighbor Mike Lennard. "But you just never know under these circumstances."  The Associated Press contributed to this report.
As water recedes and flows east onto the Colorado plains — revealing toppled homes, buckled highways and fields of tangled debris — rescuers are shifting their focus from emergency airlifts to trying to find the hundreds of people still unaccounted for after last week's devastating flooding.