Sinkhole risk in Howard County, MD: No soluble rock mapped

What this means before you buy

No soluble bedrock is mapped here, so natural sinkholes are unlikely. Collapses from broken pipes or old mines are a separate risk.

That works out to roughly 1 of Howard County's 251 square miles on soluble rock, 1 of them with the rock at or near the surface. With about 339,668 residents (1,354 per square mile), most of the county is built up, so a mapped unit is likely to sit under somebody's street. The figures come from 558 map points about 0.7 miles apart, so a pocket smaller than that can be missed or overstated.

Worth reading for this county: how these percentages are measured, and the warning signs that apply anywhere.

Counties around Howard County

The nearest county rated sinkhole country is Jefferson County, WV, about 50 miles west. 2 of the 6 closest counties land in the same band; the ground changes quickly around here.

• Montgomery County, MD 17 mi southwest · 0% at surface
• Baltimore city, MD 17 mi east · 0% at surface
• Baltimore County, MD 21 mi northeast · 8% at surface
• Carroll County, MD 22 mi north · 2% at surface
• District of Columbia, DC 25 mi south · 1% at surface
• Anne Arundel County, MD 27 mi southeast · 15% at surface

The rock underneath

The largest mapped soluble unit here is the Cockeysville Marble (marble), Late Precambrian (?) in age, covering about under 1% of the county.

Against the rest of Maryland

Howard County ranks 15 of 24 in Maryland for soluble rock at the surface, and sits above 53% of US counties on that measure.

• Washington County 61%
• Calvert County 47%
• Allegany County 24%
• Prince George's County 22%
• Anne Arundel County 15%