After disasters like the Oso landslide in Washington State, a common question is why people are allowed to live in such dangerous places. On the website of Scientific American, for example, the blogger Dana Hunter wrote, “It infuriates me when officials know an area is unsafe, and allow people to build there anyway.”

But things are rarely simple when government power meets property rights. The government has broad authority to regulate safety in decisions about where and how to build, but it can count on trouble when it tries to restrict the right to build. “Often, it ends up in court,” said Lynn Highland, a geographer with the United States Geological Survey’s landslide program in Golden, Colo.

Her agency provides scientific information about geologic features and risks, but it has no regulatory authority, and state and local regulations are a patchwork, she said. When disaster strikes, people find that their insurance policies do not cover landslides without special riders that can be ruinously expensive.

“We tell people ‘buyer beware’ ” when buying or building a home, Ms. Highland said, because risk disclosure requirements vary so greatly from state to state and even from county to county.