Summer days can be hot — 90s and even 100s — so an early start is smart. On my first morning I was in search of the Emerald Pools, three crystal-clear ponds accessed by a climb that's just steep enough to make you appreciate chances to rest.

As the trail snakes up the mountain, it becomes difficult to decide whether to look down or up. Below meanders the North Fork of the Virgin River, responsible for excavating Zion Canyon many millions of years ago. Above, the vermilion cliffs rise at angles that seem impossibly steep.

After a mile or so the first of the pools appears, and the rewards are immediate — refreshing water to soak your feet, great slabs of red rock to rest upon and thick forest cover for shade. Water seeps from the rocky walls. A narrow waterfall sprays from high above.

The pools are a pretty easy climb, but don't let them be your gauge. Other trails offer significantly greater challenges.

Ed and Terry Tennison of Austin, Texas, found that out firsthand on a hike to Angels Landing, which earned its name apparently because it's so steep no one but an angel could land on its peak.

"We saw a guy pointing to the peak and he said, 'We're going there,"' Ed said. "I just started laughing. But we did go there."

Park literature refers to the Angels Landing hike as strenuous.

"There's almost a ledge connecting one peak to another," Terry said of their experience. "There are sharp drop-offs on both sides. It's not two people wide. And it's steep."

Fortunately, chains along the steepest parts of the trail offer a little security.

"And it's something I really wanted to hang onto," Ed said. "At some point I started laughing at the word 'hike.' It was more of a climb."

"Which we now have a term for," Terry said. "Clike."

Back on safer ground, the Tennisons remembered one other thing from their ascent: "awesome views."

I met the Tennisons one morning on another hike, a two-mile walk with ranger Holly Baker called "On the Edge of Survival."

Sounds dicey, but it wasn't our survival we were worried about. More about plants and animals and how they endure in this difficult land.

"It's a pretty harsh landscape," Baker said.

Zion stretches through parts of the Mojave and Great Basin deserts as well as the Colorado Plateau. The area receives less than 14 inches of rain a year. "Plus the constant sun really adds to the harshness," Baker said.

How, then, can you account for the rich diversity of plant and animal life? More than 900 plant species can be found at Zion, the park Web site says. It's the richest array in Utah, along with 78 species of mammals, 291 types of birds and 44 species of reptiles and amphibians.