Here is a new, rich resource for K-12 teachers and students from the US Geological Survey (USGS). The Learning Web provides online lesson plans, activities, tutorials (some downloadable and printable in .pdf), and links to references dealing with interdisciplinary studies of natural science. For example, the Exploring Caves section (1-3 level) covers the basic geology of caves, life habits of cave-dwelling organisms, and cave safety and conservation. Other topics explored on the Learning Web include maps, climate, wildlife, earth processes, and more. Learning Web culls pages appropriate for K-12 instruction from the USGS's vast online collection of factsheets, data, and program sites, allowing teachers and students to spend time learning rather than searching. However, because this site is so full of information, it can be tricky to navigate and important sections can be missed, so try using their search engine to find specific topics. Note also that elementary content is much more abundant here than secondary.