The origin of the phrase “hit rock bottom”

Christine Ammer, The American Heritage Dictionary of Idioms, second edition (2013) has this entry for rock bottom:

rock bottom The lowest possible level, absolute bottom, as in Wheat prices have reached rock bottom. This idiom alludes to the presence of bedrock that prevents digging farther down. {Late 1800s}

Presumably, the digging that Ammer has in mind is digging through dirt. I remember as a child watching my grandfather use a two-handled post-hole digger to excavate holes for a new fence line on his farm. When the implement hit the limestone substrate, that was the end of the digging because he had reached rock bottom.

Use of 'rock bottom' in a literal sense

Instances of "rock bottom" in the literal sense of bedrock are quite common in nineteenth-century U.S. publications. For example, an article by John Hale on salt resources in West Virginia, excerpted in George Atkinson, History of Kanawha County: From Its Organization in 1789 Until the Present (1876):

After many unexpected difficulties and delays, the gum ["a well-formed, hollow sycamore tree, with four feet internal diameter, sawed off square at each end'], at last, reached what seemed to be rock bottom at thirteen feet ; upon cutting it with picks and crowbar, however, it proved to be but a shale or crust, about six inches thick, of conglomerated sand, gravel and iron. Upon breaking through this crust the water flowed up into the gum more freely than ever, but less salt.

As this instance indicates, "rock bottom" doesn't refer simply to rocky material but rather to solid bedrock.

Early use of 'rock bottom' in a figurative sense

Although Ammer dates idiomatic use of "rock bottom" to the late 1800s, I have found instances from 1865 onward. Some early instances involve the idea of a firm foundation rather than an economic nadir. For example, from "The Pacific Railroad," in the New York Tribune (October 20, 1865):

We hope soon to hear that the obstacles which have hitherto prevented the payment to this enterprise [the transcontinental railroad] of the subsidy stipulated by act of Congress have been happily removed, and that the work is henceforth to be pushed forward with ample means and resolute energy. Let us once get our Currency back to rock-bottom, and we shall insist on the construction thenceforth of at least one mile per day of the main track of the Pacific Road till it is finished.

Others, however, use the term in the sense of (as Ammer puts it) "absolute bottom"—the sense in which most people use the idiom today. From "Our Letter from Washington, D.C.," in the [San Francisco] Daily Alta California (May 1, 1865):

So those who would gladly build houses in cities are obliged to pay greenback prices for labor and materials, and sell or rent the houses, when completed, at gold prices; and this deters thousands from building, as it ought. Journeymen and laborers say with reason, "We must have high wages, because every thing is dear"; but this will not enable the house-owner to command corresponding rents next fall or spring—or will only effect this by reducing the erection of new tenements to a minimum. Is it not clear that coming right down to rock bottom would be best for all these?

From "Business Prospects," in the Ashtabula [Ohio] Weekly Telegraph (November 24, 1866), reprinted from the New York Tribune (again):

Now, then, is the time—if Congress and the Treasury could be induced to think so—to resume specie payments,—Those who are not ready never will be. If a year and a half of peace [following the Civil War], with n abundant Revenue and a diminishing debt, have not suffice for preparation, twenty years would not answer any better. In fact, there are to-day more debt and more pecuniary interest in the way of resumption than there were in June, 1865. We shall never resume unless we try to ; and whenever we really try we shall resume. And, since we are to have a season of declining prices and stagnant trade, why not resolve to go down to hard-pan at once? Let us resume—there is nothing wanted but the will—and have specie prices for labor, produce and goods. Then, thousands will invest in railroad making, building, &c., &c., who are now deterred by the consideration that what cost $15,000 will be worth but $10,000 when we get down to rock-bottom, as we surely must and shall. Do let us descend from the clouds and stand once more on terra-firma. If this was ever right, it is right generally, and is especially right now.

And from "Resumption—Two Ways," in the [Philadelphia, Pennsylvania] Evening Telegraph (November 29, 1867):

But, had we resumed a year ago, we should all have done a better business since than we have done. Prices of all sorts—wages included—would, from the start, have been twenty to forty per cent. lower than they have been; but, having gone right down at once to rock bottom, we should have thenceforward proceeded without peril or fear. Our manufacturers would have sold their stocks on hand at a nominal loss; but they would not have been steadily losing ever since, by buying cotton (for instance) at 30 cents per pound and selling it in fabrics when it has fallen to 25 or 20.

Early idiomatic use of 'rock bottom' as a compound modifier

References to "rock bottom prices" also appear as early as 1865. From a rather mystifying advertisement in the Cambridge [Massachusetts] Chronicle (March 25, 1865):

Great Battle Between Uncle Sam and the Yellow Boy, and a Bloodless Victory Won.

For full particulars, how Yellow Boy was defeated, how he tried to rally, and each fall proved more disastrous, how he pulled his friends, BUTTER, PORK, SUGAR, FLOUR, AND TEA, all along down with him, we advise you to consult the prices of the above Goods at BOYDEN'S, Corner of Main and Proapect Streets, who will sell you a shade lower than elsewhere. We are determined to sell at ROCK BOTTOM PRICES. — PROOF — Call at 483 Main Street, and examine prices and quality.

And from an item in the the Rural New Yorker, reprinted in the [Albany New York] Cultivator & Country Gentleman (October 13, 1870):

Now, if our information is correct, the prospect is that larger shipments of American cheese will be demanded for England the coming fall and winter than ever before. The crop in America is by no means so large as was anticipated early in the season. Putting all these items together, we cannot but think that cheese has already touched 'rock bottom' prices, and that an advance may with reason be expected.

By 1891 "rock-bottom prices" was a recognized American idiom. From James Dixon, Dictionary of Idiomatic Phrases (1891):

Rock-bottom prices—the lowest possible price. F[amiliar].

The largest stock of United States stamps of any dealer, at rock-bottom prices.

In a prefatory note titled "Explanation of Signs," Dixon reports that the designation "Familiar" means "The phrase is used in familiar conversation, but is not admissible in polite society."

Early idiomatic use of 'reached rock bottom' and 'hit rock bottom'

An instance of "reached rock bottom" appears in L.U. Reavis, St. Louis, The Commercial Metropolis of the Mississippi Valley (1874):

Prices have declined since last year, which accounts for the increased orders for goods; and now having reached "rock-bottom," close buyers can purchase their spring stock without fear of a decline. Prices are fully ten per cent cheaper than last year, and selling prices by Mr. Meyer are governed on the same basis.

And another appears in an advertisement for Rivet & Partridge Dry Goods, in the Indianapolis [Indiana] News (November 3, 1877):

ANOTHER REDUCTION has been made in the price of BLACK SILKS. We have now reached rock bottom; an inspection will convince you. We will duplicate any $2.50 Black Silk for $1.50, or will make you a present of a pattern. This is plain language, and can not fail to be understood.

The earliest match I've been able to find for the exact phrase "hit rock bottom" is from C.A. Jenkens, The Story of Pot Hooks: Or, Society as Seen by a Backwoods Philosopher (1892):

Mrs. Cyclops.—Oh! dear. You have concocted so many schemes that proved valuable only for the genius displayed in their concoction, that I have despaired of valuable results. You know, Doctor, you thought your novel would bring you a fortune, but somehow the publishers didn't take to it ; and you invented a phonetic alphabet, which you fancied princes and kings would adopt throughout the world, but the expense of getting it out nearly ruined us. Still. let's have the scheme.

Dr. Cyclops.—But I've hit rock bottom now; something tangible, solid, sure.

This instance is striking because the speaker is using "rock bottom" in a positive sense, although the author may be having the speaker misuse the idiom for humorous effect.

More typical is the following instance from a headline in the Wichita [Kansas] Daily Eagle (July 22, 1894):

HIT ROCK BOTTOM: Wheat Sinks and Fails to Rise Again: Lowest Price Known Since Present System of Trading Commenced. September Delivery Don to 54 1-4—Weakness Attributed to Lower Cables, Liberal Receipts, Favorable Weather and Disappointing Exports.

That's a farmer's life for you: you finally get a year with really good weather, and prices for your crop fall to rock bottom.

Early non-economic idiomatic use of 'rock bottom'

As for early non-economic figurative use of "rock bottom," here is an instance from "400 Oddfellows and Wives Attend," in the Hammond [Indiana] Times (April 30, 1912):

Instead of 200, the number prepared for by the East Chicago Odd Fellows who gve a big "doings" last night, 400 Odd Fellows and their ladies invaded Odd Fellows hall in response to the blanket invitations that were issued.

While greatly appreciating the compliment paid them by the guests swarming in upon them, for a moment the heart of Dr. Jacob Goldman, master of ceremonies, sank to rock bottom, when he bethought of the fine lunch that would afford abundance for the expected 200, but would be somewhat skimpy to put it mildly, for double that number. For a momently only, however.