Right now CrowdRise is only set up for credit card donations, which are processed safely and securely by PayPal Giving Fund and WePay.
If you want to make a donation by cash or check, you can give that to the organizer of the campaign instead. Make sure to make your check out to the benefiting charity.
The campaign organizer can add this contribution to their CrowdRise fundraiser manually as an Offline Donation* and then submit all cash and check donations received to the charity at the end of their fundraising period.
*offline donations may not be enabled on certain Challenges or Events, in accordance with their rules.