Wiltshire Wildlife Trust has put out an 11th hour plea for help after the group who normally assist with car parking had to pull out.
The trust's big fundraiser of the year, the Sarsen Trail sponsored walk and Neolithic Marathon from Avebury to Stonehenge stone circles, takes place on Sunday and they have been left high and dry at the last moment.
Organiser Derek Gard said: "We need six helpers from 8am until 3pm on Sunday to direct people where to park at Redhorn Hill, which is just outside Urchfont.
"If you are able to help or could even offer part of the time I'd be delighted to hear from you. If you are part of a group such as Rotary or Lions and could help out with this as a group it would really solve a problem for me."
If you can help ring the trust on (01380) 725670.
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