Book excerpt: This is the second edition of our popular and comprehensive guide to the natural history of Massachusetts' four western counties, with more than 400 full-color photographs, maps and illustrations. Everything from bears and beavers to snakes and spiders is covered. Learn about the region's geology, its rivers and mountains. Find out how it was formed by the ice age and volcanic activity. Learn about the first human residents. There are charts showing when wildflowers bloom and when butterflies are on the wing. There are checklists of common birds, trees, wildflowers and butterflies. There is also a calendar showing when events in nature happen through the months in the four counties.