Sinkhole risk in Monmouth County, NJ: Mostly deep or small

Mostly deep or small

Some soluble rock, mostly deeply buried or in a small share of the county.

On soluble rock: 13%
At or near the surface: 13%
Buried under cover: 0%

What this means before you buy

Sinkholes are uncommon here; watch for new depressions after heavy rain or leaking pipes.

That works out to roughly 63 of Monmouth County's 468 square miles on soluble rock, 63 of them with the rock at or near the surface. With about 647,520 residents (1,383 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 528 map points about 0.9 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 Monmouth County

The nearest county rated sinkhole country is Union County, PA, about 159 miles west. 1 of the 6 closest counties land in the same band; the ground changes quickly around here.

Middlesex County, NJ 17 mi northwest · 0% at surface
Richmond County, NY 19 mi north · 0% at surface
Kings County, NY 26 mi northeast · 0% at surface
Union County, NJ 27 mi north · 0% at surface
Mercer County, NJ 29 mi west · 0% at surface
Ocean County, NJ 30 mi south · 1% at surface

Which formation it is

The largest mapped soluble unit here is the Vincentown Formation (sand), upper Paleocene, Selandian in age, covering about 9% of the county. Next is the Mt. Laurel Formation at 5%.

Against the rest of New Jersey

Monmouth County ranks 2 of 21 in New Jersey for soluble rock at the surface, and sits above 70% of US counties on that measure.