Editing Canonsburg, Pennsylvania (section)

===20th century===
In 1903, the Washington and Canonsburg Railway Company linked the two towns with a trolley line. The company was bought by the ''Philadelphia Company'' in 1906, later becoming part of the [[Pittsburgh Railways|Pittsburgh Railway Company]], linking through to Pittsburgh as part of their [[interurban]] service in 1909.<ref>{{cite book |title=Canonsburg – Images of America |last=Grefenstette |first=Jerry |year=2009 |publisher=Arcadia Publishing |isbn=978-0-7385-6533-0 |page=46 |url=https://books.google.com/books?id=vr31Qfo34g0C|access-date=October 18, 2009}}</ref> The line closed on August 29, 1953, with the last three trolley cars travelling south through Canonsburg to the [[Pennsylvania Trolley Museum]] in 1954 shortly before the track was removed.

In 1911, South Canonsburg was [[annexation|annexed]]. On August 26, 1911, 26 people were killed in the [[Canonsburg Opera House disaster]]. A [[Shouting fire in a crowded theater|false shout of "fire"]] triggered a panic that killed twenty-six people.<ref>{{Cite news|title=THEATRE DEATHS DUE TO NARROW STAIRS|date=August 28, 1911|work=The New York Times}}</ref>

The [[Canonsburg Armory]], [[Hawthorne School (Canonsburg, Pennsylvania)|Hawthorne School]] and [[Roberts House (Canonsburg, Pennsylvania)|Roberts House]] are listed on the [[National Register of Historic Places]].<ref name="nris">{{NRISref|2010a}}</ref>

The Standard Chemical Company operated a [[radium]] refining mill from 1911 to 1922 on a {{convert|19|acre|m2|adj=on}} plot of land. From 1930 to 1942, the company purified [[uranium]] ore. [[Marie Curie]] was invited to the United States in 1921 and was given an honorary degree by the [[University of Pittsburgh]], and one gram of radium.

From 1942 to 1957, Vitro Manufacturing Company refined uranium and other rare metals from various ores and onsite residues, government-owned uranium ore, process concentrates, and scrap materials. The government bought the uranium ore from Vitro and used it in the [[Manhattan Project]]. Waste from incomplete extraction and other [[metallurgical]] processes accumulated during the site's long history. About 11,600 tons of mill tailings were moved to railroad property near [[Blairsville, Pennsylvania|Blairsville]] between 1956 and 1957. After the closure of Vitro, the site was used by the [[United States Atomic Energy Commission|U.S. Atomic Energy Commission]]. The site was then used by the Canonsburg Pottery Company, operated by the George Family, for land and clay.

The Canonsburg mill site was designated in the 1978 Uranium Mill Tailings Radiation Control Act as eligible for federal funds for clean up. It was the only uranium mill east of the Mississippi River to receive funds. In a $48 million cleanup project, the mill site and 163 nearby properties in Canonsburg were remediated. Residual radioactivity was consolidated into a covered, clay-lined cell at the Canonsburg mill site, which is fenced and posted.