Also, refer to chapter 14 for summarizing records, especially page 14-11. Select By Theme using Intersect should be used carefully. Meeting of line features is an intersect. If you use the intersect operation, all inside counties will be selected but so will all counties that touch the eastern edge of the western states, those of the adjacent states. Be careful on the sequence of separation.
Counties are Completely Within states.
States Completely Contain counties. Useful, especially when constructing a layout and returning to the View page. However, you must have the table open so that Layout recognizes it. The Corps of Engineers maintains some river facilities in the U.S., such as locks, erosion controls, etc. Of course, it needs to cooperate with the states.