California Underground: A Guide to Caves, Mines and Lava Tubes (Paperback) (ISBN-13: 9781591932307)

Jon Kramer is an adventurer first, and also a geologist, writer, climber and surfer (but not necessarily in that order, depending on the surf). He received his Bachelor of Science degree in geology at the University of Maryland and has pursued life as an adventuring paleontologist ever since. His interests are quite varied and include all things natural. In addition to popular travel and adventure writing, Jon has published scientific papers on critters as ancient as 2 billion year-old bacteria and as young as 12,000-year-old mammoths. Jon travels extensively with his wife Julie, sometimes settling down for a rest in Minnesota, Florida, California and interesting points in between.

Julie Martineza is an explorer, naturalist, freelance artist and formal art instructor. Her appreciation for insects, plants, rocks and fossils started in childhood with a collection that has grown throughout her life. Julie graduated from the University of Wisconsin, Stevens Point, with a degree in Fine Arts and Biology. She initially worked as an illustrator for the medical field but in the late 1980s began a freelance career, which she has enjoyed ever since. Julie's work is featured in many textbooks, journals and museum exhibits throughout North America. She is also a staff teacher at Minnesota School of Botanical Art. When not teaching, she travels with Jon, exploring the wilds of the world.