Why Does My Auger Stop at Two Feet?

What you have hit

The USDA soil series named after this county — the Minidoka series — is described as moderately deep to a duripan, well drained, formed in loess and alluvium from mixed sources. Its defining feature is a white, indurated duripan with many continuous silica-cemented laminations, occurring at depths of 26 to 40 inches, with depth to the duripan ranging from 20 to 40 inches.

A duripan is a diagnostic soil horizon cemented by illuvial silica into a subsurface hardpan. It is firmly cemented and, in the USDA’s own language, restricts soil management.

Neighbouring series around Rupert behave differently again: Portino, Banbury and Trevino carry bedrock at 10 to 40 inches. North and east toward the lava beds, you are into basalt at whatever depth it happens to sit.

So when your auger stops dead at 26 inches on a 36-inch hole, nothing has gone wrong. You have reached the layer this county is named for.

Why it matters more than people think

A fence post resists being pushed over by bearing against the soil along its buried length. The deeper the post, the longer the lever resisting the overturning force, and the relationship is not linear — depth buys disproportionately more resistance than width does.

A post that stops on top of the pan is sitting in the loose loess above it. There is very little competent material holding it, no matter how much concrete went in the hole. It will feel solid on install day. It will feel solid all summer. Then a spring wind loads the panel, the whole concrete plug rotates in the soft material, and the fence leans.

This is the single most common cause of fence failure we are called out to in Minidoka County, and it is almost always traceable to a hole that stopped where the digging got hard.

How it should be done

Probe before quoting. A few test holes along the line tell you whether the pan is at 22 inches or 38, and whether it is consistent. On lots near the lava-bed edge it can vary within a single fence line.

Break through, do not stop on it. A rock auger, a hydraulic breaker, or in lighter cases a heavier machine with a proper bit. The post needs to sit in or below the pan, not on it.

Match depth to the panel above it. A 6-foot solid privacy panel catches roughly twice the wind of an open picket fence and needs depth accordingly. On exposed ground the honest answer is often deeper than the standard third-of-post-length rule of thumb.

Gravel base, then concrete. A few inches of compacted gravel under the post gives water somewhere to go. A duripan does not drain — that is the point of it — so a post sitting in a sealed concrete cup in a hole with no drainage is a post standing in water every irrigation season.

Reduce spacing rather than fight the ground. Where breaking through is genuinely impractical across a whole run, closer posts distribute the load and are often a better answer than fewer, deeper ones.

What to ask a bidder

This is the question that separates people who work this ground from people who do not:

“What do you do if the auger stops at two feet?”

Good answers describe equipment and an approach. Poor answers are vague, or explain why it will not be a problem. A contractor who has never hit the duripan has not built many fences in Minidoka County.

Ask them to write down: post depth, post size, concrete volume per post, and what happens if they hit the pan. Those four lines are the difference between two quotes that otherwise look identical.

Bottom line

The auger stopping at two feet is normal here and it is not a reason to stop digging. The post has to go through the pan, not sit on it — and any quote that does not account for that is quoting a different fence from the one you want.

Call (208) 732-2816 and we will probe your line at the estimate, so the price reflects the ground you actually have.