Kelly Butte Natural Area (English Wikipedia)

"Memorial Stone history". Multnomah County Sheriff's Department. Archived from the original on June 18, 2006. Corrections Supt. Edward Diedrich and Corrections Powderman Charles Hall were killed May 24, 1924 in an accidental explosion at the Kelly Butte Rock Quarry. The officers, as well as a prisoner, who was also killed, were setting explosives when the explosives prematurely detonated killing all three and injuring several other inmates.

nationalmap.gov

"Kelly Butte Natural Area". Portland Parks & Recreation. Retrieved December 14, 2010.
"Sign-In Form".
"Vegetation Unit Summaries for Kelly Butte National Area (KB)" (PDF). Portland Parks & Recreation. July 29, 2009. Retrieved December 14, 2010.

Blackbourne, Nick (May 1, 2013). "Kelly Butte". The Southeast Examiner.
Hall, Tim (April 1, 2013). "Kelly Butte Makeover". The Southeast Examiner. Archived from the original on May 14, 2013. Retrieved May 14, 2013.

"Memorial Stone history". Multnomah County Sheriff's Department. Archived from the original on June 18, 2006. Corrections Supt. Edward Diedrich and Corrections Powderman Charles Hall were killed May 24, 1924 in an accidental explosion at the Kelly Butte Rock Quarry. The officers, as well as a prisoner, who was also killed, were setting explosives when the explosives prematurely detonated killing all three and injuring several other inmates.
Hall, Tim (April 1, 2013). "Kelly Butte Makeover". The Southeast Examiner. Archived from the original on May 14, 2013. Retrieved May 14, 2013.

"Aged Pioneer Dead Plympton Kelly Succumbs to Stroke of Paralysis. Came To Oregon In 1848" (PDF). The Oregonian, published as the Sunday Oregonian. September 16, 1906. Retrieved May 14, 2013.