The Dayrock Mining Company, eventually to become one of the main producers of lead and silver for the Day interests, was originally incorporated November 30, 1923, under the name of Stratton Mines Company for the purpose of acquiring and operating mining property and a millsite held by Stratton & Stratton, a partnership. Apparently the Days and their associates were the major stockholders from the start, owning over a third of the outstanding shares. The original directors of Stratton Mines Company were Jesse Freeman, president; William J. Stratton, secretary; and James A. Wayne. On February 14, 1924, the board membership was increased from three to five and Jerome J. Day and Frank M. Rothrock elected to fill the new vacancies. On January 6, 1925, William J. Stratton was replaced on the board by James J. Murphy who died in the following year and was succeeded by John Wourms on May 1, 1926. Henry L. Day replaced Wayne on May 13 of that year and F. Wallace Rothrock succeeded Freeman, the last of the original directors, on November 21, 1927. Thus by 1928 Strattons Mines Company no longer had any connection with William J. Stratton or the Stratton & Stratton partnership, except as a business rival, and a special meeting of the Stratton Mines Company directors held on October 3 resolved to change the name of the firm to the Dayrock Mining Company.

The Dayrock mine was located in the Placer Center mining district on the west side of Nine Mile Gulch, approximately three miles north of Wallace, Idaho. Profits were great enough to offer five dividends of about three cents per share between 1928 and 1932, when low metal prices during the Great Depression halted ore production. In 1935 the board of directors decided to restart the mine and levied an assessment of .006 mills per share, but within a year the Dayrock was again making large profits and sent to its stockholders a dividend of two cents per share. Between 1936 and 1947 Dayrock stockholders received four more dividends for about two and one-half cents per share each.

In 1930 the Option Mining Company, consisting of the Pacific and the Ohio Lodes, was purchased for 36,000 shares of Dayrock stock. Other Dayrock purchases included 15 percent of the Press Times Publishing Co. from Hercules Mining Company and the California Consolidated Mining Company.

From 1928 onward the Day interests always held a majority of the Dayrock shares and controlled the board of directors. In 1943 S.F. Heitfeld succeeded Jerome Day who had died, and in 1945 Eleanor Day Boyce succeeded the late John Wourms. Otherwise, the composition of the board remained the same for nineteen years. After the merger of the Dayrock Mining Company into Day Mines Inc. in 1947 the Dayrock mine continued to be a major producer of lead and silver until its closure in 1977.