The squirrels in your landscape may be tree squirrels or ground squirrels. If you aren't sure which kind they are, visit the UC IPM web site to read about Tree Squirrels and Ground Squirrels.
If you know your arboreal visitors are tree squirrels, you can read more about them and their management in the newly revised UC IPM Pest Note: Tree Squirrels by UC Cooperative Extension Specialist, Dr. Roger Baldwin.
You might also be interested in these two previous articles and blog posts: “Tree Squirrel or Ground Squirrel: What's the Difference? Part I and Part II by Dr. Niamh Quinn, UC Cooperative Extension Human-Wildlife Interactions Advisor, San Diego, Orange, and Los Angeles counties.