UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K/A

Amendment No. 1 to Form 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (date of earliest event reported): August 22, 2016

U.S. Silica Holdings, Inc.

(Exact name of registrant as specified in its charter)

Delaware

(State or other jurisdiction of incorporation)

Registrant’s telephone number, including area code: (301) 682-0600

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Explanatory Note

On August 22, 2016, U.S. Silica Holdings, Inc., a Delaware corporation (“U.S. Silica” or the “Company”), and U.S. Silica Company, a Delaware corporation and a wholly-owned subsidiary of the Company (the “Purchaser”), completed the purchase of all of the outstanding units of membership interest (the “Acquisition” or the “Unit Purchase”) of Sandbox Enterprises, LLC, a Texas limited liability company (“Sandbox”), pursuant to the terms of the previously announced Membership Unit Purchase Agreement, by and among the Company, the Purchaser, Sandbox, each of the owners of membership units of Sandbox (the “Sellers”) and Sandy Creek Capital, LLC, as representative of the Sellers (the “Purchase Agreement”). The Form 8-K filed August 24, 2016 (the “Initial 8-K”) omitted the financial statements of the business acquired and the pro forma combined financial information as permitted by Item 9.01(a)(4) and Item 9.01(b)(2) of Form 8-K. This amendment to the Initial 8-K is being filed to provide the financial statements and pro forma financial information required by Item 9.01 of Form 8-K. The Initial 8-K otherwise remains the same and the Items therein, including Item 9.01, are hereby incorporated by reference into this Current Report on Form 8-K/A.

The consideration paid by the Purchaser to the Sellers at the closing of the Unit Purchase consisted of $70,480,000 of net cash, subject to customary post-closing adjustment and 4,195,180 shares of common stock of the Company. A portion of the cash consideration has been deposited into escrow to support the post-closing purchase price adjustment and the Sellers’ indemnification obligations.

(a)(1) Audited financial statements of business acquired

The audited financial statements of Sandbox Enterprises, LLC as of and for the year ended December 31, 2015, including the notes thereto, are filed herewith as Exhibit 99.1.

(a)(2) Unaudited financial statements of business acquired

The unaudited financial statements of Sandbox Enterprises, LLC as of and for the six months ended June 30, 2016, including the notes thereto, are filed herewith as Exhibit 99.2.

(b) Pro forma financial information

The unaudited pro forma condensed consolidated financial statements of U.S. Silica Holdings, Inc. as of June 30, 2016, and for the year ended December 31, 2015 and for the six months ended June 30, 2016, including the notes thereto, are filed herewith as Exhibit 99.3.

(d) Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: September 30, 2016