The Journal of San Diego History
Fall 1979, Volume 25, Number 4
Thomas L. Scharf, Editor

by David C. Burkenroad

General Division Winner, San Diego History Center 1979 Institute of History

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A LITTLE MORE THAN TWENTY miles southeast of San Diego, within the boundaries of the Mexican land grant Rancho Jamul, a curious and substantial masonry structure stands isolated at the foot of a low hill. The structure houses two octagonal kilns, a brick smokestack rising more than thirty feet above them. Limestone and clay from a deposit on the hill behind were once burned in these kilns by the Jamul Portland Cement Manufacturing Company, an enterprise created during the boom of the 1880s.

The limestone deposit was soft, almost pure calcium carbonate in the form of caliche leached out of the surrounding soil.1 Its location was undoubtedly known to the native Kumeyaay (Diegueño) and subsequently to the Franciscans of Mission San Diego, who used Rancho Jamul as a sheep pasture.2 It has been suggested that during the 1810s, the missionaries used Jamul limestone in the construction of their dam and aqueduct at Mission Gorge. But actually, lime kilns were erected at deposits closer by, along the San Diego River.3 The Picos were probably the first settlers to make use of the limestone. Pío Pico was the first grantee of Rancho Jamul, and his brother Andres settled there during the 1830s. Mexican calcinistas commonly made quicklime and whitewash for domestic purposes.4

Captain Henry S. Burton was the first documented user of the deposit. He had come to California in 1847 as co-commander of the First Regiment of New York Volunteers. In directing the military takeover of Baja California, he met his bride-to-be, María Amparo Ruiz, granddaughter of a pioneer soldier-settler. After marrying in Monterey, the couple went to San Diego, where Burton bought Rancho Jamul. Burton had some engineering skill, and in 1856 the San Diego Herald reported that he had men burning the limestone on his ranch to make lime.5

Burton was subsequently transferred East, where he died in 1869. In June of 1870 his widow María arrived in San Diego to settle her husband’s estate.6 Burton had died without a will, and his estate included the as-yet-unpatented 8,926-acre Rancho Jamul.

Within weeks María Burton arranged with Pío Pico to substitute her and her children’s names for that of her husband’s in the title to Rancho Jamul.7 In 1875, after protracted litigation against squatters and mortgage holders, María Burton succeeded in acquiring title to the Mexican land grant.8 Although the estate of Henry Burton was not settled until 1891,9 the land was used again as collateral for mortgages, and its title changed hands repeatedly.

In 1879, María Burton and her lawyers began a decade-long project of petitioning for a substantial homestead out of the still-unsettled estate of Henry Burton.10 The limestone deposit and the future site of the cement plant were located within the eventually confirmed 986.6-acre homestead.11 At the time, the mortgage of Rancho Jamul was held by Wallace Leach, a prominent lawyer, and John Capron, a former transportation magnate. These men objected to the widow’s petition, perhaps because the homestead encompased a potential railroad right-of-way between San Diego and the East.12 The Probate Court sustained their objections. But Mrs. Burton appealed and won her case in 1889, when the California Supreme Court ruled that the petition was valid although it did not affect title to the Rancho itself.

Just before the case was decided María’s thirty-six-year-old son Henry, who had been born on Rancho Jamul, made a preliminary evaluation of the cement-making potential of the limestone deposit located on his mother’s homestead. Two financial backers, C.W. Lyke and Benjamin Macready, were in association with him.13

Although the real estate boom in San Diego had peaked and collapsed in 1887. demand for cement in California had begun rising in 1886, and in 1888. about two million dollars’ worth was sold.14 In San Diego, entrepreneurs such as Elisha Babcock, who was building the Hotel del Coronado, found that they could not order cement without going through San Francisco importers. John Spreckels, an heir to his uncle Claus’ sugar fortune, was intrigued by the commercial possibilities. In 1887, he sailed his yacht from San Francisco to San Diego, where he established the Spreckels Brothers Commercial Company and built a wharf at the Bay capable of handling large quantities of coal and building materials.15 But cement nevertheless continued to be difficult to obtain locally.16

At the time, all of the cement imported was foreign, much of it artificial European Portland-so named because of its resemblance to a yellowish-white building limestone from the Isle of Portland in England.17 The profitable grain trade with California allowed incoming ships to cheaply carry cement around the Horn, often practically as ballast. An attempt to manufacture Portland cement at Santa Cruz had failed a decade before,18 and because of the large quantities of foreign cement being bought, the State Mineralogist was encouraging its local manufacture.19 Burton undoubtedly read his report of 1888.

By August, 1889, Burton and his associates had persuaded Carl Leonardt,20 a cement chemist and engineer living in Los Angeles, to make and test cement from the Jamul limestone deposit. The San Diego Union reported that Leonardt prepared a sample that was as good as some of the foreign Portland.21 Apparently satisfied with the suitability of the limestone deposit and expecting that a railroad connection would eventually be built to it, Henry Burton and his mother, C.W. Lyke, Benjamin Macready and Carl Leonardt formed the Jamul Portland Cement Manufacturing Company on September 12, 1889.22 The company acquired the necessary real estate a month after incorporation, when María Burton conveyed to it two plots of land out of her newly confirmed homestead, one containing the limestone deposit (59.4 acres) and the other being an eight acre site by Jamul Creek for the proposed cement plant.23

The company did not succeed at once in attracting sufficient investment capital to begin construction of a plant. Capitalists were certainly available in San Diego during the 1880s, but local manufactories, even with the twenty percent duty imposed on foreign cement, were not in a position to compete easily with the well-developed economies of England and Europe. But by January of 1890 new stockholders had invested in the company and taken over its direction. Warren Wilson, founder of the San Diego Sun, was elected company president.24 In February, he and the German engineer left for the East to raise additional capital,25 and also to obtain information on manufacturing methods and costs in Pennsylvania, where David O. Saylor’s Coplay Cement Manufacturing Company had recently produced the first American Portland Cement.26

At Jamul, the cement plant began to be constructed in April of 1890, under the supervision of Henry Burton.27 Carpenters began by constructing a boarding house for themselves and the future workers. The approximately seventy-foot-high masonry structure that still stands was constructed out of the locally available metavolcanic stone. Within, two octagonal kilns were built side by side and lined with layers of common brick and firebrick.

While a shipment of fireclay to finish lining the kilns was awaited, the necessary freighting arrangements were made. Although proposed since 1854, no direct transcontinental railroad had been built eastward from San Diego Bay. Two local railroads had nevertheless been constructed in the general direction of the cement deposit, the National City and Otay, and the San Diego, Cuyamaca and Eastern. Throughout the 1880s it was rumored that one or the other local railroad would be extended towards Campo and Yuma through Jamul Valley.28 In January of 1890, the president of the National City and Otay even considered extending the railroad to the still-unbuilt cement works.29 But other than switches at Bonnie Brae to facilitate wagon-freighting to and from Jamul,30 no track was built.

Six bids were made for a contract with the Jamul Cement Works to haul both fuel for the kilns and boiler and its intended production of cement.31 The Cuyamaca and Eastern got the job. By February, 1891, wagon-freighter Joseph Nickerson had hauled more than 260 tons of Australian coke the thirteen miles between the railroad station at Spring Valley and the plant.32 But wagon-hauling proved more difficult than expected, and the railroad was forced to relinquish its contract to the National City and Otay.33 The road from Sweetwater Valley was longer, but the grades were apparently easier. The new contract, however, specified that the cost of hauling the cement to the railroad was to be borne by the cement company itself.34

In the winter of 1890-91, a gravity-operated, hand dumpcar trolley system was installed between the deposit on the hill and the plant. It was reported that as a loaded car was sent down the hill, it hoisted up the empty one. In this way, the first 600-800 tons of quarried limestone material were transported to storage bins at the plant. Because the limestone was a soft caliche, little effort was required to extract it from the ground.35

Besides having kilns for burning limestone, the cement plant resembled a “combination of a quartz and a flour mill.”36 Like a quartz mill it required crushers for grinding up the raw materials. According to the Union,the various grades of ground limestone at Jamul would be run in elevators to bins from where they were “weighed out to the right proportions.”37 After being mixed, the materials were wetted and dropped into a brick machine. The so-called “bricks” of raw cement were dried in a room heated with steam-fed pipe.

The kilns were designed to be loaded through doorways at the top with cement bricks and alternating layers of coke, and to be fired continuously. The mass of bricks and coke was to be burned until the raw materials began to vitrify. If the firing went well, as the coke fuel was consumed, clinker, a substance resembling lava, dropped to the botton of the kilns.38 The clinker was then ground between horizontal French flourmilling buhrstones.39 The resulting powder was cement.

The kilns were fired up in March of 1891.40 After a few weeks of trial runs, a satisfactory product was obtained.41 Pavement in San Diego was made with it.42 Several carloads were sent to Carl Leonardt, who was involved in the construction of a beet sugar refinery in Chino.43 This apparently created a demand for Jamul cement, for five additional so-called pot kilns were erected.44 These smaller kilns with boiler-iron casings were connected to the rest of the plant by a wooden platform and went into production in July.45

The demand created by the construction of the Chino refinery was short-lived. The organizers of the Jamul Cement Works had hoped to eventually produce 1000 barrels (200 tons) of cement per day.46 But the daily capacity of the plant was reportedly 150 barrels,47 and the National City Record reported maximum productions of 40 barrels in the summer of 1891.48 Besides several wagon freighters, the plant employed only about three dozen men, most of whom lived at the company’s boarding house.49

The crucial railroad spur was not built, and it cost about as much to haul cement by wagon the dozen or so miles to the railroad at Sweetwater Valley as it did to ship it around the Horn to the Bay.50 Labor costs were also high.51 Moreover, the same high demand for cement that had led to the development of the local manufactory had also led to “overstocking by a speculative European movement.”52 In 1889, cement actually glutted the California market. In San Diego, the Spreckels Brothers Commercial Company was importing up to 200,000 barrels of Portland at a time.53 The incorporation in September, 1891, of the California Portland Cement Com-pany,54 which is still in operation today, further undermined the finances of the Jamul Cement Works. The building boom in Southern California had subsided, and the nation as a whole was headed towards the Panic of 1893. Any financial support for the improvement of the Jamul Cement Works dried up.

By July of 1891 the company was forced to take out a mortgage on its property.55 The plant was in production then, but unable to make profits. A few weeks later it executed notes totaling almost $10,000 to the California National Bank of San Diego.56 Additional notes were mishandled,57 the bank itself folded in November,58 and the Jamul Portland Cement Manufacturing Company was on the verge of bankruptcy. By October, after having manufactured only about 5,000 barrels of cement,59 the plant was out of operation.60

Early in 1892, its suppliers began to sue the Jamul cement company for more than $8,000.61 A bankruptcy sale was forced onto the company when J.F. Ramsey, who held the mortgage, sued for nonpayment.62 Ramsey himself bought the Jamul Cement Works and its quarry for $10,000 in a public auction held in March of 1893.63 Thus ended the only attempt at manufacturing cement in the hinterland of San Diego Bay.

Besides having made serious economic miscalculations, the developers of the Jamul Cement Works had faced numerous technical problems. The major difficulty in producing Portland cement was obtaining a consistently suitable mixture of raw materials and firing it efficiently at the high temperatures required to create its essential constituent, tricalcium silicate.64 Most plants went through several years of development before perfecting the manufacturing process.65

Despite its intentions, the Jamul Portland Cement Manufacturing Company did not succeed in producing high-quality Portland. The Portland sample manufactured by Leonardt in 1889 was made by a trained chemist and under controlled conditions; this was apparently not possible at the Jamul Creek plant.66

Contemporary geological reports classify the cement simply as “hydraulic” (water-resistant).67 The local newspapers certainly would have praised it had it been a better-than-average cement. The National City Record only guardedly stated, “It is said that the product is proving very satisfactory.”68 Carl Leonardt, who had lent his reputation to the company, was reported to have considered the cement as “eminently satisfactory,” but no measure was given of its tensile strength as had been for the sample he produced in 1889.69 At the Chino sugar refinery the cement seems to have been used merely as mortar in brick walls.70 Otherwise, the cement seems to have been used primarily for pavement,71 which does not require great durability in the mild climate of Southern California.

Although the tensile strength of the Jamul cement is not known, its chemical composition is.72 A measure known as the Cementation Index indicates that it was on the borderline between Portland and the so-called “natural” cements.73 Natural cements, which had been manufactured in the United States since early in the nineteenth century, were made from deposits, like the one in Jamul, which contained mixtures of calcium carbonate (limestone), silica, alumina and other oxides in proportions resembling Portland’s; they were usually not as strong as the carefully proportioned artificial cement.74 Natural cements could generally be fired at lower temperatures than those required for making Portland, but the Cementation Index indicates that unless the Jamul cement was fired at temperatures approaching 1200° Centigrade, it would be unsound due to the presence of large amounts of free lime; this may have been one of the causes of the poor quality of the Jamul cement.75

The kilns at Jamul reflect the precarious nature of the San Diego Portland cement enterprise. The pot kilns resembled Campbell kilns, which were inexpensive and commonly used at American natural, but not Portland, cement factories.76 At the time the Jamul plant was being constructed, German Portland cement manufacturers had developed so-called Schoefer and Dietzsch kilns with specially designed firing chambers;77 Schoefer kilns were being installed at the Coplay cement plant in the Lehigh Valley of Pennsylvania.78 But the San Diego entrepreneurs apparently did not have the expertise and capital necessary to build the elaborate kilns, and they settled for a more primitive German design known as a Schachtofen (shaft kiln).79 The Jamul kilns were not the most modern, but their large size and impressive looks may have been designed in part to show that the Jamul Cement Works were there to stay, to inspire the confidence of stockholders and railroad men, and to attract capital for further development.

After the company’s failure, the Jamul Cement Works was never put into operation again.80 Early in the twentieth century, while John Spreckels owned Rancho Jamul, the limestone deposit was “not found to be of sufficient promise to justify further operation.”81 By 1906 most of the plant was dismantled.82 By this time, the California Portland Cement Company at Colton and other large plants were in production, and the Jamul deposit was not only too small to be profitably developed but still lacked a railroad spur.

Because the Jamul Cement Works was not developed, the masonry kilns were not replaced with more advanced ones. Although cracks have developed and firebricks are missing from the linings, the kilns have stood largely undisturbed since 1891. Because of their primitive design they might prove to be the only ones of their kind still standing in the United States.83 The Jamul masonry kilns are California’s oldest extant cement-burning kilns. They are the vestiges of the boomtime capitalists of Southern California who were willing to invest with a young man who wanted to build a factory on the place of his birth; and a fitting monument to the hopes of nineteenth-century San Diegans.


1. W.A. Goodyear, “San Diego County,” Annual Report of the State Mineralogist (hereinafter abbreviated as ARofSM) 9 (1890), p. 139; Harold F. Weber, “Mineral Resources of San Diego County,” California Division of Mines and Geology County Report 3 (1963), p. 180. The Annual Report of 1890 (p. 309) gives the following composition for the deposit:

Calcium carbonate (limestone) 84.28%
Silica 11.86
Alumina 1.18
Carbonate of Magnesium 1.19
Carbonate of alkalies 1.15

Weber gives the following:

  North Quarry South Quarry
Calcium Oxide 48.49% 44.24%
Silica 8.32 13.34
Alumina 1.16 3.20
Magnesia 1.23 1.40
Iron Oxide .28 .61

2. Unless otherwise indicated, information on the early history of Rancho Jamul and also biographical information was obtained from files at the San Diego Historical Society (SDHC) Library and Manuscripts Collection. The record of Burton’s acquisition of Rancho Jamul and certain other title information was kindly provided by Dr. Ray Brandes from the Title Insurance and Trust Company.

3. Fred Green, “The San Diego Old Mission Dam and Irrigation System” (San Diego, 1933), pp. 77-78 (Typewritten.).

4. Ian Smith, “A History of the Mining Operations at Mt. Slover, Colton, California” (Colton, California, 1978), p. 198 (Typewritten.).

5. San Diego Herald, 26 April 1856, p. 2.

6. San Diego Union (SDU; Weekly), 9 June 1870, p. 2.

7. California Reports 68, p. 488.

8. San Diego County (SDC) Patent Book 2, p. 121.

9. SDU, 4 January 1891, p. 5.

10. California Reports 63, p. 37. Subsequent appeals are summarized in 64, pp. 428-9 and 79. pp. 490-5.

11. SDC Book of Deeds 58, p. 167, 154, p. 263, 185, p. 376.

12. This was suggested to the author by Dr. Ray Brandes.

13. SDU, 17 May 1889, p. 5.

14. ARofSM 8 (1889), p. 865; SDU, 1 August 1889, p. 8.

15. H. Austin Adams, The Man John D. Spreckels (San Diego: Frye and Smith, 1924), p. 162; John C. Monteith, Directory of San Diego and Vicinity for 1889-1890 (San Diego: Gould Hutton and Co., 1889), p. 3; SDU, 29 September 1887, p. 4, 5 January 1890, p. 10.

16. SDU, 29 September 1889, p. 4.

17. ARofSM 8 (1889), p. 865; Robert W. Lesley, History of the Portland Cement Industry in the United States (Chicago: International Trade Press, 1924), pp. 43, 88.

18. Oliver Bown, “Cement,” California Division of Mines and Geology Bulletin 176 (1957), p. 119; Robert A. Kinzie, Jr., Santa Cruz, personal communication, 1979.

19. ARofSM 8 (1889), P. 869.

20. Press Reference Library, Notables of the West (Los Angeles: International News Service, 1913), p. 373.

21. SDU, 1 August 1889, p. 8.

22. Articles of Incorporation , Jamul Portland Cement Manufacturing Company, SDC CIerk, File # 616.

23. SDC Book of Deeds 154, p. 263.

24. SDU, 1 January 1891, p. 12.

25. SDU, 2 February 1890, p. 8.

26. ARofSM 9 (1890), p. 310; Benjamin L. Miller, Contribution of David O. Saylor to the Early History of the Portland Cement Industry in America (n.p.: Pennsylvania German Society, 1930), pp. 12-17.

27. National City Record (NCR) 30 April 1890, p. 2; SDU, 2 April 1890, p. 5, 8 April 1890, p. 2, 23 April 1890, p. 6, 9 May 1890, p. 8.

28. Spencer Menzel, “Paper Railroads of the 90’s” (San Diego, 1943), pp. 1-10, 22-4, 63-5 (Typewritten.);NCR, 23 May 1889, p. 3; SDU, 26 June 1887, p. 3; 19 August 1887, p. 3,7 May 1889, p. 6.

29. SDU, 18 January 1890, p. 6.

30. NCR, 1 May 1890, p. 6.

31. SDU, 28 October 1890, p. 8.

32. G.P. Grimsley, “The Portland Cement Industry in California,” Engineering and Mining Journal, July 20, 1901, p. 71; SDU, 4 February 1891, p. 5; Parker T. Wheaton, Odometer Survey, 1894, San Diego Public Library (Diagram copy.).

33. NCR, 5 February 1891, p. 5.

34. Ibid.

35. SDU, 12 December 1890, p. 5, 28 February 1891, p. 8.

36. ARofSM 8 (1889), p. 869.

37. SDU, 30 March 1890, p. 2.

38. ARofSM 8 (1889), p. 874.

39. Grimsley, Engineering and Mining Journal, 1901, p. 71; Spencer B. Newberry, “Natural and Artificial Cements,” U.S. Geological Survey Mineral Resources of the United States Calendar Year 1891 (Washington, D.C.: Government Printing Office, 1893p, p. 534.

40. NCR, 5 March 1891, p. 2.

41. SDU, 17 May 1891, p. 5.

42. Ibid.

43. Carol Jensen, “Chino’s Agricultural Development,” Pomona Valley Historian 9 (October 1973), p. 141; Press Reference Library, Notables of the West, p. 383.

44. SDU, 17 May 1891, p. 5.

45. NCR, 2 July 1891.

46. Mining and Scientific Press (San Francisco) 62 (no. 14, 1891), p. 216.

47. NCR, 19 March 1891, p. 2; Storms, ARofSM 11 (1893), p. 383.

48. NCR, 30 July 1891, p. 2, 1 October 1891, p. 2.

49. Reports indicate that between 32 (SDU, 30 March 1891, p. 2) and 40 men (Storms, ARofSM 11 (1893), p. 383), worked at the plant. See also Louis Merz, Oral History Project interview transcript, 1957, SDHC Library; Frances Lockwood, Oral History Project interview transcript, 1957, SDHC Library.

50. NCR, 12 March 1891, p. 2; Storms, ARofSM 11 (1893), p. 383. In 1887, ship freight was $.75-1.10 per barrel (ARofSM 8 (1889), p. 865.

51. At current California wages for lime and cement workers (U.S., Census Office, Report on Manufacturing in the United States at the 11th Census, vol. 8, p. 349), the labor cost per barrel would be above the $1.00 recommended by the State Mineralogist (ARofSM 8 [1889] , p. 869).

52. ARofSM 9 (1890), p. 310.

53. SDU, 5 January 1890, p. 10.

54. ARofSM 8 (1889), pp. 504-5; John Brown Jr., and James Boyd, History of San Bernardino and Riverside Counties (Chicago: Lewis Publishing Company, 1922), vol. 1, p. 225; U.S., Geological Survey, “Mining Resources, 1889-1890,” Miscellaneous Documents of the House of Representatives, 1892, p. 463.

55. SDC Book of Mortgages 68, p. 190; Superior Court, District 3 (SC) Case # 7035.

56. SC Case # 7329.

57. SDU, 28 February 1892, p. 5.

58. SC Case # 7329.

59. Newberry, Mineral Resources, 1893, p. 536.

60. George J. Locke, “Report of the General Manager of the National City and Otay Railway.” Fifth Annual Report of the Board of Directors of the San Diego Land and Town Company to the Stockholders, December31, 1891 (Boston: R.H. Blodgett, 1892), p. 16.

61. SC Cases #s 6612, 6629, 6945, 7442.

62. SC Case # 7035.

63. SDC Book of Deeds 222, p. 287.

64. F.M. Lea, The Chemistry of Cement and Concrete, rev. ed. (London: Edward Arnold Ltd., 1956), pp. 112-21. Other problems included controlling the firing, unclogging the kilns, refiring underfired clinker, repairing the buhrstones, etc. See Uriah Cummings, American Cements (Boston: Rogers and Manson, 1898) p. 247; Edwin C. Eckel, Cements, Limes, and Plasters (New York: John Wiley and Sons, 1905), pp. 234, 238; Q.A. Gillmore, Practical Treatise on Limes, Hydraulic Cements, and Mortars (New York: D. Van Nostrand Company, 1890), p. 64; Newberry, Mineral Resources, 1893, pp. 529, 534; Ian Smith, retired mining contractor, California Portland Cement Company, personal communication, 1979.

65. For an amusing but telling comparison, see Lesley, History of the Portland Cement Industry, p. 127.

66. This was suggested to the author by Messrs. K.C. Hayden and Ian Smith of the California Portland Cement Company. According to Mr. Hayden, Mr. Wilson Hanna of that company wrote an account in which the Jamul cement was referred to in a deprecatory, and perhaps quite accurate, manner.

67. Goodyear, ARofSM 9 (1890), p. 139.

68. NCR, 5 March 1891, p. 2.

69. SDU 17 May 1891, p. 5.

70. Anthony Lehman, “The Sugar Beet Builds a Business,” Pomona Valley Historian 5 (April 1969), p. 79; Chino Valley Champion, 13 March 1891, p. 2.

71. SDU. 17 May 1891. D. 5.

72. ARofSM 9 (1890), p. 309. The composition was as follows (Accuracy unknown):

Lime 65.20%
Alumina 5.24
Silica 24.00
Iron Peroxide 2.21
Magnesia 1.20
Alkalies 1.00
Carbonic acid 1.00
Sulphuric acid .20
Total 100.05

73. Eckel, Cements, Limes, and Plasters, p. 70. The Cementation Index is calculated as follows:

2.8 x % Silica + 1.1 x % Alumina + .7 x % Iron Oxide
% Lime + 1.4 x % Magnesia

The Index of the Jamul cement was 1.1. Portland cements ranged from 1.00 to 1.15; natural cements from 1.15 to 1.60.

74. ARofSM 8 (1889), p. 869.

75. Eckel, Cements, Limes, and Plasters, pp. 194-293. Analysis of the slag adhering to the kiln linings may determine the temperature at which it was fired.

76. Cummings, American Cements, p. 236; Eckel, Cements, Limes, and Plasters, p. 22

77. Pierre Giron, “The Burning of Portland Cement,” Proceedings of the Engineers’ Club of Philadelphia 10 (July 1893), pp. 197-221.

78. Dr. Mahlon H. Hellerich, Director, Saylor Park Cement Industry Museum, personal communication, 1979.

79. A.J. Francis, The Cement Industry 1796-1914-A History (London: David and Charles, 1977), p. 236; Frederick H. Lewis, “Plants in Germany,” The Cement Industry (New York: The Engineering Record, 1900), pp. 212-3; Carl Naske, Die Portland-zementfabrikation (Leipzig, Germany: Theod. Thomas, 1922), pp. 151-5. The exact functioning of the Jamul kilns has not been determined. A technical description is projected.

80. In 1895, however, the Clarks of nearby Dulzura made some cement from the deposit for the foundations of the new house they were building (Dorthy Clark Schmidt, Pioneering in Dulzura (San Diego: Robert Knapp, 1963), p. 54.

81. Frederick J.H. Merrill, The Geoand Mineral Resources of San Diego and Imperial Counties (Sacramento: State Printing Office, 1916), p. 54.

82. Merz, Oral History Project interview transcript, 1957, SDHC Library; SDU, 20 July 1902, p. 9.

83. As has been pointed out, Schoefer kilns were installed at the Coplay Cement Manufacturing Company in Pennsylvania. The distinctive natural cement kilns of the Rosendale area of the Hudson Valley were circular and without a chimney stack (Ann Gilchrist, Footsteps Across Cement—A History of the Township of Rosendale, New York [n.p.: By the Author, 1976), pp. 45-57. After the 1890s, rotary kilns were used almost exclusively at American Portland cement factories.