Geologically, it is a syncline fold consisting of highly eroded Precambrian metamorphic rock.

[1] These hills were formed from deposited sediment in a shallow sea 1.7 billion years ago.

The Baraboos are composed of resistant Precambrian quartzite (a metamorphic rock) which has formed an erosional remnant or Monadnock, resulting in topographic prominence.

These formations were buried by Paleozoic sedimentary strata and are still being uncovered by the erosion of the softer, overlying rocks.

[4] Bluffs at Lower Narrows carved by the Baraboo River expose contacts between the quartzite and younger volcanic rhyolite.