Richard Brusca says he has always emphasized that the Sonoran Desert is much more than the cacti and creosote of the Tucson Basin.

"The Sonoran Desert is so much bigger and more complicated and diverse," he said.

Brusca, a zoologist and marine biologist, has spent most of his research trips on the shores and seas of the Gulf of California. The Sonoran, he says, is a maritime desert.

Brusca's wife, Wendy Moore, is an entomologist who specializes in beetles, but says you can't study those critters without knowledge of the plants, animals, soils and rock in their ecological niches.

Moore's arthropod studies caused the couple to take a closer look at the Santa Catalina Mountains and all the Sky Island ranges that make up what naturalists call the Madrean Archipelago, a gap in the continental divide, populated by mountain ranges separated from each other by desert floor.

Their book, "A Natural History of the Santa Catalina Mountains, Arizona, With an Introduction to the Madrean Sky Islands" combines their research with that of friends and colleagues to tell the story of the most-visited mountain range in the region.

Most Tucsonans know that driving up the Catalina Highway to Mount Lemmon takes you through a series of biomes, from desert floor to conifer forest. It's the equivalent of driving at sea level from Mexico to Canada.

One chapter of this lushly illustrated book takes that trip with you, encouraging you to take your time, stop along the way and appreciate the amazing diversity of the mountain we usually call by the name of its highest peak, Mount Lemmon.

The book, published by the Arizona-Sonora Desert Museum Press, is spiral-bound so you can take it along with you and see the mountain anew through the eyes of a couple of very observant scientists.

A shorthand version of their suggested stops

• Stop 1 | Soldier Trail: In the front range of the Catalinas, at 3,255 feet, Soldier Trail is a classic example of upland desert, with saguaros, palo verde and mesquite trees, acacia, ocotillo and desert scrub.

• Stop 2 | Babad Do'ag Vista: From here, at 3,555 feet, you can see a panorama of Sky Island mountain ranges - Rincons, Santa Ritas, Sierritas and Santa Catalinas. It's also a great view of the city of Tucson.

• Stop 3 | Molino Canyon Overlook: Paved and unpaved trails from this parking lot at 4,150 feet, give a view of the transition from upland desert to grass and oak woodland. In the canyon bottom, the wetter microclimate allows growth of cottonwood, ash, walnut, mulberry and sycamore.

• Stop 4 | Molino Basin: This wide basin at 4,750 feet, is part of the Romero Pass fault which separated the front range of the Catalinas from its high country peaks. This is mostly Emory oak grassland, with other oak species in the riparian areas. Here, you have left the upland desert vegetation behind.

• Stop 5 | Middle Bear Canyon: In summer, this is among the first shady spots for lunch. Here, at 5,900 feet, pine trees make their first appearance, mixed still with oaks, cypress and juniper. Pines dominate the wetter, cooler north slopes.

• Stop 6 | Windy Point Vista: The biggest paved parking lot along the highway, at 6,600 feet, affords a rest-room stop and a spectacular view of the entire Tucson valley from a shelf of granite outcrops favored by photographers and rock climbers.

• Stop 7 | San Pedro Vista: Your first chance to see the other side of the mountains - the northeastern slopes of the Catalinas and the green ribbon of cottonwoods where the San Pedro River flows. At 7,350 feet, this is the edge of the pine-oak woodland and the start of the pine forest.

• Stop 8 | Palisades Visitor Center: At 8,000 feet, you are in the thick of a forest of Arizona pine and ponderosa pine, which will dominate the landscape for the next few miles. Bathrooms are available and the visitor center has books, maps, information and special-use passes.

• Stop 9 | Mount Bigelow Road/Bear Wallow: The old growth mixed conifer forest beneath Mount Bigelow in Bear Wallow at 8,100 feet, boasts Douglas fir, southwestern white pine, white fir and, of course, ponderosa pine. A rough dirt road takes you past the University of Arizona's observatories to the communications towers and a fire watch at the 8,497-foot summit.

• Stop 10 | Mount Lemmon/Summerhaven: This is the most densely populated part of the mountain. The village of Summerhaven with a smattering of restaurants and stores and a rebuilding enclave of second homes sits at about 8,400 feet. Mount Lemmon, with its ski lift, observatories and forest of communication towers, tops out at 9,157 feet. Here, the damage from the 2003 Aspen Fire is dramatic. In the unburned sections, tall pines mix with aspen and fir trees.