Simplicity

These are rebuses of a particular kind of thing, where the relative positioning of the letters is important.

These are rebuses that clue a string that is a city name plus a letter. Without the extra letter, the city names fit the enumeration.

In order to extract, you'll want to rearrange the extraneous letters onto the final rebus. The cities are alphabetically ordered, so you'll want to find something that encodes this positional data.

Try plotting the extra letters on where the cities are on a map.

The top part works semantically; what's a common word that is often used to mean the four-letter sequence of letters on top? The bottom part is phonetic. You'll end up with another North American geographic feature.