At Harrop go down Harrop Proctor Road about two blocks to McConnell Road and head west. McConnell will become Lasca Creek Road.
Alternatively, make like the masses and get to the park from the Nelson side, on the west. To accomplish this, in the north west corner of Nelson, get onto Gordon Road heading east, go north on Bealby Road, which will become Bealby Point Road, and continue as far as you can go. A third alternative is to boat up (or down) the West Arm to the park.
Largely undeveloped, this is a wilderness park with essentially no facilities. It you like to get away from all the RVers and civilization in general, this is the place for you. The park itself is 25,319 hectares in size and runs along the south side of the West Arm for nearly three miles, and up the hills for nearly ten miles to the peak of Ymir Mountain. Roads in to the park are not maintained in the winter, making this essentially a summer park.
Though there are camping fees for provincial parks, the camping areas here are wilderness campsites and are walk in sites from boat/canoe landings and I believe there is no fee for wilderness sites. As such, don't expect showers, toilets, picnic pavilions and the like because you won't find them.