Mandurah Mayor Paddi Creevey and family members, including wife Kathleen, unveiled the sign on the 2½- hectare natural bush reserve on the corner of Caspian Drive and Agonic Way.
With legendary boundless energy, Mr Beacham, who died in February aged 96, pursued issues of inappropriate development or where environmental degradation had occurred.
An accomplished photographer, he could always be relied on to provide photographic evidence of good and bad environmental outcomes, and his photographs went to politicians, newspapers and were put on public display.
Making no concession to age or impaired vision, he wrote hundreds of submissions, attended countless meetings, workshops and study days, supported fundraising stalls and showed dogged determination in exposing violations of environmental codes of practice to decision-makers.
The reserve is representative of the outcomes Mr Beacham sought to achieve during his involvement with Peel Preservation Group of which he was an active member for more than 60 years.
Mr Beacham was a Freeman of the City, a life member of the Peel Preservation Group, an active member of Mandurah Historical Society and Mandurah Community Museum.