Each of the four players was a member of the Timbers' USSF Division-2 Pro League team in 2010. Danso and Goldthwaite helped Portland's backline rank among second-division leaders in fewest goals allowed and shutouts last season.
"The four players we've added today can play at the next level in Major League Soccer," said Timbers head coach John Spencer. "It doesn't matter which division you've played in previously, if you're good enough, you're good enough. I think these guys have the ability to make an impact at the next level.
"We have signed a Gambian international in Futty and a young Ghanaian international in Kalif. James is a Haitian international, who has the potential to be one of the top young midfielders in the league. Kevin is a player I've known and worked with and has won a championship in Houston. He brings us great leadership qualities in the back. Their resumes and pedigrees are first-class."