The Boulder County Clerks Office has an online index to their records. ( http://icris.co.boulder.co.us/login.jsphttp://icris.co.boulder.co.us/login.jsp ) It is a gold mine, although sometimes names etc get cut short. But with the information you can write to them and get copies of the certificates, last time I checked it was $3 each. (One note - the date for marriage certificates was the recorded date which could be a few days after actual ceremony)
Some of the things - Mary Eliza. Campbell married William Wagn. Gillard on 9 March 1893. There were dealings with a Charles Campbell, A.E. Campbell & Amanda E. Campbell (same?). Appears he had an interest in a tungsten mine. Florence Cam. Gillard married Lawrence W. Sunderlin 30 April 1919. Gladys E. Gillard married Edwin G. Nelson 14 June 1920. Frank Gillard married Eva Barnarad 8 August 1921. Mary Louise Gillard married James Clarenc. Hetzer 28 Dec 1923. There is mention of a William W. Gillard Estate on 13 April 1925, so he died before that date. There is also mentioned, in context with the family, a Charles Mart. Gillard and a William F. Gillard. Charles Mart. Gillard married Ruby Irene Tollefson on 2 May 1927. There is mention of a Grace Vione. Gillard as a minor in 1935. Inheritance tax was paid on the Mary E. Gillard estate on 12 May 1937 (so she died prior, possibly 2 years earlier). Louise Hetzer was the Administratrix of the Mary Gillard estate.
You need to go look through that site. There are a number of "decrees quieting title" where everyone with any possible interest in a deed has to sign off. One takes up almost an entire page and list alot more Campbells & Gillards plus a large number of other people.
Also, I recently subscribed to Ancestry.com that has scanned images of all censuses. The 1920 and 1930 are also indexed so if I find a name it is easy to look them up. In 1920 (ED30, Precinct 13, Boulder County, page 4A) it was : William W.age 49emigrated 1891, naturalized born Canadafather born Englandmother born IrelandFarmer M. Elizaage 46born Coloradofather born U.S.mother born U.S. Mary L.age 20ColoradoTelephone Operator Gladys E.age 16ColoradoTelephone Operator Grace N.age 2 7/12 (listed as daughter)Colorado
Mary E. Gillard is alone in the 1930 census (Boulder, Boulder County, ED44 page 4B). Here she says her father was born Indiana and her mother is still U.S. Don't see Grace on the index.
And finally, The Boulder GenWeb site has the Nederland Cemetery online and no Gillards.
Charles & Amanda Campbell are buried in Columbia, but no sight of any Gillard. Strange. But there are a Mountain View Memorial Park and a South Boulder Catholic cemeteries which don't have online indexes.