“Practice,” he broke in.

“Uh-huh.” But she hadn’t finished. “You got it right if the quake’s from magma shifting in the Sour Creek dome. But if it’s from the Coffee Pot Springs dome… That’s farther away, so the quake would have to be bigger.”

“Didn’t feel that far off,” Colin said. “The jolts were sharp, not roll-roll-roll the way they go when they’re a long way out.”

“Here’s hoping you’re right.” She didn’t sound-or look-happy. And she had her reasons: “The Coffee Pot Springs dome literally just showed up on the map a little while ago, and it’s swelling like a stubbed toe. It’s like the magma’s found some new weak area that gives it a path up toward the surface.”

Colin knew what magma was: the hot stuff that spewed out of volcanoes. Here in Yellowstone, it was also the canned heat that kept geysers boiling and hot springs bubbling. He had trouble putting those two things together, though. “What would happen if it did?” he asked.

“Did what? Get to the surface?”

“Yeah. Would it be… a volcano, like?”

“Mm, kind of.” Now the look on her face said he’d disappointed her. He’d known something about earthquakes, so she’d hoped he would know something about volcanoes, too. That shouldn’t have bothered him. If anybody’d had practice disappointing women, he was the guy. But, obscurely, he didn’t want to disappoint this one. She went on, “Like a volcano the way a Siberian tiger’s like a kitten, maybe.”

“Huh?” he said brilliantly. To try to salvage things, he added, “I’m not staring at your chest. I’m just trying to read your name badge.”

That got him a crooked grin. “Well, it’s a story. I’m Kelly Birnbaum.” He gave her his own name. She came up and shook hands over the boardwalk railing. He’d known police sergeants with a less confident grip. She looked west. “I bet you went to Old Faithful before you came here.”