Q. Should a local geographic place-name retain the original apostrophe, such as Lund’s Gulch in Snohomish County, Washington?
A. The official name is Lunds Gulch (no apostrophe), which can be verified by entering either form of the name into the GNIS Domestic Names Search Application available from the US Board on Geographic Names (BGN). The BGN doesn’t normally allow such apostrophes in place-names—as we noted in our answer to question 5 in “Chicago Style Workout 65: Apostrophes” at CMOS Shop Talk. (One well-known exception is Martha’s Vineyard.)
If you’re concerned about using the correct spelling, leave the apostrophe out. But if, for example, you’re writing a novel and want to follow the local custom, the apostrophe seems relatively common for that local landform—for example, on this page for “Lund’s Gulch” at the website for Lynnwood, Washington. Just be sure to alert your copyeditor to any such preference.