Complex sentence: Almost abandoned in 1876 when word of the much larger gold strikes in Deadwood Gulch spread, Custer City later became an established city, if smaller and less wealthy than the Northern Hills cities of Deadwood and Lead.
Split into simpler sentences: Almost abandoned in 1876 when word of the much larger gold strikes in Deadwood Gulch spread, Custer City later became an established city. It has had a smaller population and been less wealthy than the Northern Hills cities of Deadwood and Lead.